I snagged this for my cell phone. I upgraded from an old 2gb SD card I've been refusing to replace for the last 4 years. The old card does not specify the class, and it was the cheapest I could get; so I have a feeling it was the slowest . Anywho, I plugged this card in and transferred 27 songs from my PC to phone in about 20 seconds! On my old card that would have taken around 2 minutes. If you haven't upgraded your card, (because you're a cheap miser) like me, you are definitely missing out!