Summary: Card and adapter worked just fine, comes with small plastic case for storage which I like getting with my cards. Class 4 fast enough writing for MP3 player, (class 2 would be fine too), all cards read the same speed.
Summary: Just make sure you always backup your SD cards like you do your hard drives. That is all these are. They could quit working at any moment. That is what I had happened to my last one, which was a SanDisk. But it don't stop me from buying them. It lasted for 3 phones. But I always keep mine backed up every week. I have others and most are the same. They are all mass produced so you will always have a couple that don't work.
Summary: I ordered a SanDisk 64GB microSD Class 10 Ultra Card but was very disappointed to find that not only wasn't it formatted but it was ONLY 27.4 GB!!! It also won't work in the video camera it was bought for. I am returning it.