For my galaxy s4 I bought microSDHC card adata premier - Premier microSDHC/SDXC UHS-I Class10_Memory Cards_ADATA Technology this one. Here is the speed charts - Charts, benchmarks SD Cards 2014,  Sequential Write [MB/s] - its almost 20mb/s. My card is much much slower than this. I bought it from very trusted shop in my town so its impossible to be fake. The write speed when I write mp3 files (4mb avg) is 4mb/s when I copy through cable (from pc to the phone's sdcard). When I write directly to the sd card with card reader its 8mb/s. So what happens? Is anybody have the same problem? Is it normal when I use cable the speed to be slower than with card reader. Why the speed is at least 2 times slower than in tests? (the card is formated in fat32).