In answer to a few of your questions, the M9 has good gas efficiency, good range, great reliability, great price, and is one of the most skirmish worthy Pistols out there (IMO, at least).
I've owned the KJW USP, and would take the M9 (ABS or metal) any day for reliability and function. Get some extra mags, keep the resoviors sealed with silicon, keep them about half full of green gas at all times, and have a blast! I have been using a KJW M9 since I have been playing airsoft. Even before I got an AEG. Metal is the way to go for the extra 20 bucks, but make sure to NOT get the ghey grey-colored ELITE version. It's ugly. And it's grey.