I'm a big fan of the flash cards. I use them daily on my iPhone and so have to use the web as they aren't in the app.
The new buttons, while great on the large screen of a pc, have been really difficult to use on the mobile. The last release overnight though has made it now virtually impossible. The buttons now are no longer responsive and so extend way off the screen meaning that for every card I would need to scroll horizontally to rate it, then scroll back again.
Please get your developer to just take a look on his/her phone.