I wish there were a way to practice the "weak words" we've learned in Duolingo.
There's a section in the app that tells you what words you've practiced least, but there's no way to practice or review them in an actual exercise. I wish there were..
SRS is indeed fantastic.
A word of warning about Memrise: they seem to have absolutely horrible support. They completely ignore repeated queries by users on the forums or via email. If your request to cancel a subscription it would still show that you are subscribed, and they do not confirm on email that it was canceled. You'd do better without something free like Anki that you can adjust to your own needs.
I had this exact thought a long time ago, how have they still not implemented something for this, they give you a way of identifying a problem but offer you no solution, what kind of design is that? It's mildly infuriating. I assumed at some point they'd develop that page, but they haven't.
The partial workaround people have suggested doesn't work for me.