Some rather obvious comments:
Hanon can be very useful if played the right way. That is, you don't mechanically plow through them but you have to LISTEN very very carefully to ensure the absolute evenness of the notes you are playing. The whole point is to develop equality of the fingers. Start out by playing pianissimo. Also try staccato, then dotted rhythms, etc... But always LISTEN. Sometimes you can feel your fourth and fifth fingers "buckle" and produce a slightly uneven note. That's a sign for you to stop and go back and redo.
Yes, rather obvious. Or are they?
Well let us ask some questions and make some comments that should be very obvious but apparently are not. (Never underestimate the power of conditioning to foster unthinking behaviour):
Hanon can be very useful
Useful to whom? Useful for what? How much is “very” and how this “very” compares with other approaches? Surely if - as I believe – the only thing Hanon is useful for is for the playing of Hanon itself, it can only be useful to people who wish to include Hanon in their performances. To other people – who want to play real music – the third question must be answered, for if the “very” of Hanon pales – as I believe – with the “very” of working on repertory, then a person who is not interested in performing Hanon would be better off using her/his time in more productive ways.
[…] right way. That is, you don't mechanically plow through them but you have to LISTEN very very carefully to ensure the absolute evenness of the notes you are playing.
Right. This is going to be a very enjoyable task. And what aim exactly is being sought here? Ah yes, to ensure evenness of notes. But surely this is not the appropriate language to use. It will lead to misconceptions and unrealistic views of piano playing. You see,
you cannot ensure even the relative evenness of the notes. Let us go down that road, shall we? First the pitch is uneven since you are playing different notes. Next you will have unevenness of geography, since black notes are in a different tridimensional space (that is, assuming you are being a good boy and doing Hanon in all keys). Then you have unevenness of decaying (the high register in the piano has such a short decay that dampers do not need to be applied to the strings up there – just open your piano and check it out). Then you have the unevenness of volume inbuilt in the string itself.
But perhaps most importantly, why would you want to ensure absolute evenness? Which piece of music calls for absolute evenness? Surely you should be striving for
unevenness, the sort of unevenness most appropriate to bring out a particular musical conception. Ah, but for that you need a
musical context, and in Hanon there is none. Or at least Hanon did his best to subtract as much musical context as possible from his exercises, because (as Cortot, and as Dohnanyi, and as many others)
he wanted to separate the mechanism form the musicality. And now here comes you suggesting that you don´t mechanically plough through them.

Sorry, but they are
meantto be mechanically plowed through. Not only these are Hanon´s directions, as many famous pianists and pedagogues and piano philosophers (Charles Rosen to mention but one) would have you read a novel while going through this sort of exercise to relieve the boredom.

You see, what you actually mean is not “evenness” (which is impossible), but “control”. Then your “obvious” statement might even make a bit of sense. But I would still disagree that Hanon is useful to develop control.
The whole point is to develop equality of the fingers.
Surely Hanon believed that. It is right there in his preface as his main aim in donating to mankind this wonderful gift of 60 virtuoso exercises

. But now let me add an obvious observation of my own.
Have you looked at your hands recently? If not, have a good careful look and note:
1. Your fingers are of different lengths. How are you going to make them equal? Surgery?
2. Your thumb opposes the other fingers. How are you going to put it right? I guess surgery, but it may be tricky.
3. Do this simple – but enlightening - experiment.
Put your hand on a table top in a playing position (only fingertips touching the table top, nice arch under the hand)
Now bend your 3rd finger back, under the hand, at the middle joint and keep your 3rd finger middle joint in touch with the table top at all times. Now try lifting the thumb up and down without letting any finger pad lift from the table top and specially the middle joint of the 3rd finger. You should find it easy and no problem.
Again repeat for the second finger. You should also find it perfectly possible to lift the second finger and bring it down without problems.
Try the 5th finger. Again, little or no problem.
Now, try the 4th finger.
Four years ago I would tell you that it is totally impossible to even move the finger a single 10th of a milimeter from the table. In fact I would have told you, 4 years ago, that you wouldn’t be able to move the 4th finger at all in that position (because of the slips linking the tendons, bla bla bla). And
no amount of exercise is always going to change that.
However, four years ago, I was approached by a couple from Taiwan that wanted piano lessons for their little boy. And since his previous teacher was heavy on silly finger exercises that go nowhere fast, the mother was surprised that I was not giving him loads of this rubbish to practise at home. Since it is not my policy to criticise teachers, I simply showed her what I have just described above. I had the little boy have his hand in that position, and yes, he could not move the 4th finger if his life depended on it. So, I concluded, there was little point in using exercises to develop an ability that was impossible to acquire anyway. Besides, one plays the piano pressing the fingers down, not up, so again, lifting the fingers high a la Hanon is simply not required.
At that point, the mother was very curious, and she tried it herself. To my astonishment (she did not play the piano at all) she could lift her 4th finger as high as any of the other fingers. How could she? Very simple. She was a mutant (and I say that without implying any derogatory sense to the term). Although the greatest majority of the population will have the slips joining the tendons, she clearly did not have it (a characteristic shared by 0.000001% of the world population).
So, if you are able to lift your 4th finger in the position described above, don’t fool yourself: it has nothing to do with exercise, (the mother in question had never exercised that particular motion) you are simply one of the few mutants. Nor will it give you any advantage to be able to do so, since the piano is not really played with the fingers, but with a complex co-ordination of the whole body.
As for lifting each finger in turn in a normal position (that is, without the third finger bent under), again anyone can do it without any need for exercise. People who apparently cannot do it, cannot do it not for lack of “exercise” (implying the muscle strength to do so) but for lack of “knowing” how to
will a movement. Once you get this knowledge you will always be able to do a specific motion without any need for practice or exercise. The knowledge of “willing” a motion, is of course a big mystery in physiology/psychology, and no satisfactory explanation exists at the moment for how we actually do it (which is of course the mind/body problem which has dominated philosophy now for two centuries without a satisfactory, definitive answer, and has dominated religion forever with some dogmatic and completely unsatisfactory answers).
Fortunately, we do not need answers to be able to do it. However, misguided theories (like postulating the importance of exercises, when exercise really has little or nothing to do with it) can lead you down a path where results are less than optimal, while the misguided theory gets the credit.
So, again, if the whole purpose is equality of the fingers, then why bother? It is not going to happen, is it?
Start out by playing pianissimo. Also try staccato, then dotted rhythms, etc...
These are important practice variations, but unless you have a purpose (musical) to do them, they are just a waste of time.
Without aim practice leads nowhere because you have no way to know when you did enough. It is not good saying: “Start out by playing pianissimo”, and not determining what you hope to achieve by doing that. First if you don´t know what you aim to achieve, how are you going to know when you got there? Something that could be over in a couple of minutes can go on for hours a day for years to come. Furthermore, once you establish your aim and purpose, it may turn out that the methods you are using to get there may be completely inappropriate.
It reminds me of the zen story where a zen master observed one of the monks in the temple rushing every early morning to the meditation hall and leaving late at night. The zen master asked him: “How come you meditate for such long hours?” the monk replied: “because I want to get enlightened”. The master thought about this for a while and nodded his head sending the monk on his way.
The next day, as the monk was rushing to the meditation hall, he noticed the master sitting in the garden, surrounded by a huge pile of clay bricks. He had a brick in his hands and was sanding it furiously with a piece of sand paper. The student was very curious, so he stopped by and asked: “Master, what are you doing?” The master replied: “I am polishing these bricks.” “why?” “Because I want to make a mirror.”
But always LISTEN. Sometimes you can feel your fourth and fifth fingers "buckle" and produce a slightly uneven note. That's a sign for you to stop and go back and redo.
Well, which one is it? Are you going to listen and pay attention to the sounds you are producing, or are you going to “feel” the 4th and 5th fingers buckle? Or are you supposed to do both? And if this happens, why exactly is it bad? And if it is bad, the way to fix it is to go back and redo it? Shouldn´t you do it in a different way? After all, if you just repeat what you are doing surely you are going to get more of the same result, are you not? This again reminds me of the American I once met in Brazil who was trying to get some information form a local who did not speak English:
American: “Do you speak English?” (in a nice polite way)
Local: “…” (looks dumbfounded)
American: “Do you speak English” (a bit louder)
Local: “…” (looks like he does not have a clue)
American: “D-O Y-O-U S-P-E-A-K E-N-G-L-I-S-H” (real loud now)
Local: “...” (looks around for some sort of help)
American (really loud and irritated now) “*** IT! CAN´T YOU ANSWER A SIMPLE QUESTION? DO YOU SPEAK ENGLISH?”
So I intervened and told him: “Er, he is not deaf, you know, repeating it louder is not going to help if he cannot understand you”.
Likewise, repeating something for hours a day in the same way is not going to improve something that is wrong to start with. You must do something different.
Best wishes,
Bernhard.