Memrise is doing a lot of things really well regarding memory techniques.
My main issue with using them has to do with two things:
- the tendency towards literal translations, which I don't like to have on the flashcards I look at every day.
- re-using other people's flashcards, which substantially lowers their effectiveness.
Flashcards are generally only as good as the learning process that they remind you of. If you make them, that learning process is fairly extended and multi-sensory. If you don't, then it's just a quick moment of trying to figure out what on earth the other person meant.