The controller doesn't work for my Nexus 4. The only thing that works is the middle button. It will pause/play, and if I hold it down to opens up the (thus far, for me) ever so useless Google Now app. Would love to be able to next/previous songs and change volume.
What music app are you using that the controller works for? I'm using the built in one.
Typically volume buttons are for apple devices ONLY, so that's expected. Multifunction button should work for play/pause/call and long press for Google NOW. Also, double-click to skip to the next track. Every single pair of headphones I tested with my Note 2 worked that way. You can also try JAYS app (https://play.google.com/store/apps/details?id=se.jays.headsetcontrol) to configure triple-click to skip back, though you will have to play with click delay setting to get it to work.
Strangely, some of tte Xiaomi promo pictures show the headphone with HTC One, Samsung, and Xperia implying it will fully work with Android phones. Unless if real Piston does work and fake one doesn't?