I shot one in England once for the better part of an afternoon... back in, I think, 2001 or 2002 when I could still shoot a little. I seem to remember it was an MK3.
The trigger took some getting used to, but once that was sorted (I mean, I could get used to a Gamo trigger, which was a lot worse, hehheh), it was every bit as accurate as the NJR I had. It wasn't as accurate as my wife's CR-X, but then again I've never shot a rifle that was as accurate as that CR-X -- on a good day, it would do clover leafs at 50 meters indoors.
I didn't do so well with the GC2 on standers (just like the NJR), which I thought at the time might have to do with the longer lock time. The Pro Target was way easier to shoot, especially with standers and kneelers.
In terms of usability, I'd say the Pro Target was probably the better gun. In terms of longevity, not so sure.
I remember preferring the NJR over the GC2, solely because of the trigger, though. Having said that, the NJR would occasionally act up, until I ditched the original regulator in favour of a Welham reg.
I never shot the GC2 for an extended period of time, so I never noticed any weird temperature shifts. Which I would've been used to, since the NJR with the original reg would do exactly the same. I also don't know about it being pellet fussy, as I shot it with the pellets that the owner used with it.
The Filthy Pig
: Air Arms 100 (1990) + AA Olympic trigger + Welham reg + Custom Shop CS1000 stock. Status: leaking.
The Unknown Quantity
: AA EV2 Mk4. + BSA Platinum 10-50x60 + Jon Harris wheel. Status: sorted up to 25 yds.
The Limping Dog
: Air Arms Shamal (1989) + unknown origin sporter stock + Optisan Cobra 3-9x42. Status: slowly leaking; needs work.
: HW97k + Venom Lazaglide. Status: working just fine; needs scope.
with apologies to NJR100