I prefer it over Anki, personally, but only because Anki itself is so clunky in the way it handles large decks. As far as anki decks vs. memrise courses go, Anki wins on the sheer number alone. Anki's supposed to be easier to make your own cards for, too, although I haven't bothered with that for either tool.

Incidentally, 50% off of Memrise is nothing special. Keep hitting your daily goal for, like, a week on one course, and they'll offer a 50% discount. I haven't seen them go over 50% even on a special like this, though, so it's not like this isn't a decent sale. Just letting you know that that's an option if you want to support them but can't afford the full price at a time when it's not on sale.