Greetings.
With Clementi do you refer to the Sonatinas? I am familiar with them. Do them. They are very helpfull and prepare you for Mozart, Beethoven. Do Czerny. I have tried some Hanon excercises and you may do them if you'd like, I didn't like them. Scales, arps, chords, Czerny, ect is alot more helpfull. If you do like them then feel free to excercise them. From what I know about them, don't go for speed, but always for finger dexterity and relaxations.