I have the kakitorikun extension but I much prefer the original.
Version 2 is just a bit too advanced, as it's aimed at high school students I think.
It may well be using similar vocabulary but it feels more difficult somehow. The interface is a little better, but not enough to make me want to use it yet. You get a little more feedback on your handwriting as well, much more like DS美文字トレーニング
I also have 250万人の漢検 except it's the older 200万 bought in BookOff! That's hard too. Again maybe because of the target audience.
Another one I have and really liked is なぞっておぼえる大人の漢字練習完全版
http://www.nintendo.co.jp/ds/software/yokj/index.html
Aimed at adults though so the vocabulary is difficult. I don't use it as much since I bought Kakitorikun.
DS美文字トレーニング
http://www.nintendo.co.jp/ds/avmj/index.html
is also good. It's not teaching you kanji as such, it's teaching you how to write them correctly. Much stricter than Kakitorikun.
All in all Kakitorikun v1 is my favourite. Grade school is just about my level really.
I wonder if the publisher could be convinced to do an English edition. Just add keyword and shukugo translations to the dictionary section. Or just adding the ability to annotate an entry would be enough.
I prefer electronics to paper, now that iFlash has come out for the iPod Touch I could see myself buying one soon. I have tuttle flash cards but I never use them now.