I like the idea of metal buttons, but they seem to be very difficult to get right. Most that I’ve had rattled to some degree, and quite a few had sharp edges. Those that didn’t rattle were often overly tight. To me, the material matters less than being light to depress without having too many false presses, while being quiet and not protruding too far from the case. Mous gets this right, as does Apple and just a few others.