There are some tools that can be used to check your USB flash drive / thumb drive.
1. Check Flash
This utility able to show you the average read and write speeds of your thumb drive. Check Flash is very easy to use and it also can check error on your thumb drive.
2. Crystal Disk Mark
This tool can perform sequential read and write tests of your thumb drive including hard drive.
3. HD Tune
HD Tune is another disk benchmark utility that can also be used to test flash drive speeds. Unfortunately the free version will only test read speeds. However, they do have a more advanced pro version that will also test write speeds as well as other things.
4. Flash Memory Toolkit
Flash Memory Toolkit is a set of utilities for flash memory devices. Using this toolkit you can get detailed device information and erase files / recover files, backup and restore, benchmark the read and write performance of the flash drive.
5. HD Speed
HD_Speed can be used to check the speed of data transfer on your hard disks, CD or DVD ROMS and USB flash drives.