I was very impressed by the number of characters I learned quickly, but after about 2 months I stopped being able to remember more than the English meanings for the kanji. This is good for learning to recognize kanji, but as a learning tool for vocabulary, it doesnt promote long term learning. I think the problem is the sheer number of things they have you study and repeat. I did not find it easy to learn the readings or vocab words with multiple kanji or hiragana this way. I think Anki is better for actually learning vocab, but Skritter is good for learning to write Kanji and stroke order.
Cartilage! about Skritter Japanese