I haven't tried a PSP one, but i think (maybe it's just my device) that Dingoo has a really crappy d-pad, the four directions are ok, right diagonals too, but when it comes to the left ones, it really fails. I've seen a video of a guy attaching a plastiglas circle on it, and i saw images of a rubber d pad being glued to it also.
Does any of that work? Why is it that 2/4 diagonals wont work like the others?