I own a couple of these and I've tested them on several devices.  I use these cards mainly for my mobile devices.  The 64 gb has performed well on my galaxy note 2 and galaxy note 3.  I've tested the transfer rates and they are within the prescribed range.  These are not the fastest class 10 cards, but they are sufficient for storing pictures, movies, and songs. I'm able to play songs and movies off of the card without any delay at all.