I love everything about Renshuu and it's why I've made it my only app for Japanese learning – it made it so easy to quit Duolingo.
However, one feature I'd like to see here is the option to skip/replace audio questions within a quiz without switching it off completely (e.g. a button that says "I can't listen to this question right now"). Sometimes I cannot use the audio because of my surroundings and I might not have earphones with me, so I end up having to stop the lesson.
(Please let me know if this feature already exists and I just haven't discovered it).