PRB
I have a large music collection that I like to play from the phone. This allows me to put a lot more on the phone than I have in the past. I had no compatibility problems with it. Plugged it in and it worked. Can't get better than that. As far as speed goes, it's as fast as any card I've had in the phone. I have noticed no lag or other issues reading or writing to it in the phone. I don't use it outside of the phone so I can't comment on direct read/write speeds.