You must be referring to the Belkin n50 Speedpad.
If you are, then I hate to inform you of this, but the speedpad suffers quite severely from Ghost buttons. You cannot begin to count how many times I was playing CounterStrike and it threw in a button I didnt press. It only suffers from it when more then three buttons are being pressed at one time, but trust me, when playing MAME, that happens a LOT.