I purchased two of these microSDXC cards when they were on sale around Black Friday, and have been using them now for just about two months. They work wonderfully and I have had absolutely no problems with either. These SanDisk memory cards are 64 GB microSDXC class 10, UHS-1 cards, which are rated for transfer speeds up to 30MB/sec.The UHS class 1 designation is intended as an performance measure that indicates the card is capable of supporting real-time full HD video recording. Of course, this only works if you are using a device which is capable of writing to the card at those speeds, but most modern devices that offer full HD recording, such as camcorders, digital SLR cameras, and cell phones with built in Full HD recording do support this standard. The benefit of using a UHS-1 card on a UHS certified device is that you should not encounter the problem of buffering or your device stopping recording because it could not write fast enough.However, because these are extra high capacity, sdXC cards, you will need to make sure that your device can support microSDXC cards, and not simply microSD or microSDHC ones. The biggest difference is that the microSDXC standard uses the exFAT file system, rather than the FAT32 or NTFS systems. While most modern Android devices (and in fact most linux/unix devices) can handle that without difficulty some devices, such as older cameras, Android devices, and some Windows devices, may have difficulty with the format.Having said that, I've been using these in Nikon D80 & D7000 digital SLR cameras, as well as Samsung Galaxy S3 and Galaxy S Relay 4G phones without any difficulty, and they read & write fine on my computers. All in all these were a great buy and I'm very happy with them.