Confusing as usual :-)
There are 2 different versions (as far as I know)
U8510-0: 2100 Mhz only
U8510-1: 900/2100 Mhz
I haven't been able to confirm whether there are any additional hardware differences..
I own a U8510-0 but not the second model, although I've successfully flashed -1 software on it.
Incidentally, if you happen to figure out how to access all of the phone's memory contents while in the special flash mode (Vol Up+Vol Down+Power without SD card), please let me know.
On the U8800 (X5) this worked easily because there is a memory controller of some kind - on this phone (and others by Huawei) there seems to be none. I'm sure there is a trick to this.. but what is it ?