Nail Polish review SNEAKER TREAD BLACK RUBBER iPHONE
SD specs state that class 10 cards must guarantee 10MB/sec transfer speeds in various conditions, so it should exceed this out of the box under ideal conditions. This product's advertised speeds are "up to 20MB/sec" (which usually means reads).
Under diglloydTools DiskTester on my MBP, which can usually come pretty close to capping various flash device speeds:
Using test size of 2GB, 4MB at a time at start (0%), within a 30.2GB test file.
Iteration 1: writing...15.2MB/sec, reading...19.6MB/sec
Iteration 2: writing...15.6MB/sec, reading...19.7MB/sec
Iteration 3: writing...15.6MB/sec, reading...19.7MB/sec
Iteration 4: writing...15.7MB/sec, reading...19.7MB/sec
Iteration 5: writing...15.7MB/sec, reading...19.7MB/sec
So under good conditions (out of the box, large file transfer), I'm able to hit their advertised speeds, and both reads/writes are well above what is required for the spec. This agrees with several other reviews that the card is fast, with some numbers to back it up.