I hear this opinion a lot, and I'd just like to add it manages to help with some exposure and repetition at the very least. I'm sure you're more knowledgeable than myself with learning languages, but I've been using Duolingo to learn Japanese for a little while now and have managed to pick out basic hiragana and katakana here and piece together small words.

I don't have any delusions that I'll be fluent if I finish this course, but if it can help me learn the characters it's worth the time to me.