Just be careful with the no-name brand mmc cards. I bought a cheap one off eBay last month. after a few weeks, I noticed my 770 was crashing a lot. I decided to reformat my mmc card and re-clone the OS on it. When it was setting up the partitions, it found bad sectors on the mmc and couldn't finish the operation.

Ended up buying a name brand (Kingston) mmc mobile card this time, which has been good so far.