It doesn't feel very tough, but I'd have to stomp it a bunch to be sure. ProCo is usually pretty good in the reliability department, so maybe it's fine. If you want a RAT, buy a RAT, not this. The BRAT is probably as good as it gets in this price range, though. It won't hurt you none.
Volume raises and lowers volume, tone adjusts tone, and distortion adjust distortion.
Through solid-state amps I'm not crazy about it, through tubes it sounds fantastic. This may say more about the amps than the Brat, but there it is. The range of distortions is sort of comparable to a Boss OD pedal but slightly edgier at the upper end. You can get a nice range from fuzz to classic metal, harmonics are good and with a Les Paul sustain is interminable. You can get punk and grunge tones also.