If you're looking for a way to strengthen your practice, this might be it, but...
A while ago I was looking for an app that would let me practice writing kanji because writing on paper is a pain and makes my fingers tired. I tried another app and I was disappointed enough that I gave up, until now. This app let's you practice writing your kanji, and it drills you on their usage. I find the usage practice particularly useful because there it allows me to review in context several different readings of a single kanji. If you know one reading, and one use for a kanji, then you don't really understand Japanese, so this app is filling in some holes for me.
But, and this is a pretty big butt, at $2.99 for the elementary school grade 1 app, and $3.99 for the subsequent apps, which I'm assuming run up to grade 9, you could end up spending around $35 to get through all of the kanji. Is it worth it? We'll see. If you see me reviewing the other grade levels you'll know if it was for me or not.