I have 3 of these USB's now.
I have found the write speed to vary between these devices:
10 mb/s, 20 mb/s and the best 30 mb/s.
Read speed is also faster, on the faster write speed drives, minimum of 80 mb/s.
( I used 'SpeedOut' software for testing )
I do like these USB's - they are not the fastest in the world, but they are very good for the price.