I just tried it on my Axim x30 624Mhz.
I set the speed on the device in the control panel to maximun like they sugested and then started XCPUScaler. It locked up every time I went above 624Mhz. I had to take the battery out to get my device to reset.
It then told me I had used all my 15 changes and locked me out of the program.
Pretty dissapointed in it.