I'll spare you the super harsh review and just say that I think the kana (and kanji) de manga are a waste of money and don't belong in the library of a serious student. On the other hand, their yojijukugo book is actually pretty good. Probably the best source for yojijukugo that I've seen in English.
I don't think kana is that hard, and free online sources and a pencil and paper should do the trick. If you REALLY want to spend some dough, the white rabbit press kana cards are probably pretty good. Their kanji cards are excellent. But my recommendation is just use the free online sources for kana and save the money for kanji resources. Also, any decent beginner's textbook will have kana practice as well. Genki is my recommendation, but there are other good textbooks out there. If you're attracted to the manga aspect, Japanese in Mangaland actually looked pretty good. If I'd found it earlier in my studies, I probably would have bought it.
Here's one website you might try:
http://www.guidetojapanese.org/hiragana_ex.html