Which USB flash disk

Hello,

I test 3 usb flash disks : 
- the first was supermounted (bootmsg) , but the cd command freeze when  I 
try to go to /mnt/flash.
- the second was supermounted (bootmsg), but I found no files (I put 3 
files on).
- and the third worked well (supermountig ok, data access ok).

All devices are USB 2.0, all from differents companies.

So what could be the problem ? 

Best Regards,

Sébastien Dagnicourt.