Hanon is very good and there are several other finger dexterity exercises to aid trills, etc.
This could well stir up a hornets nest as we have not had any "Hanon Wars" for ages....
I had the same reaction to an unqualified assertion of fact like Hanon is very good. My own stance on Hanon is that it's "good" if it's used judiciously and produces positive results.
"Concert performance level." Who knew?