I'm using a Squire Strat with a piece of shit Gorilla practice amp, so I don't expect much as far as sound quality goes, but the SGX has served me fairly well. I've heard a lot of people rag on the sound quality, and in truth it's definitely not the best sound available, but if you learn to edit your own patches you'll get a LOT more use out of this machine. For whatever reason, ART just didn't put a lot of time or effort into programming their presets, or if they did they were going totally for the grunge crowd. I play metal, mostly of the thrash variety, and blues of all varieties and I've been able to come up with some satisfactory custom presets just by finding one that's close to what I want, and then editing it to my specifications. This can take a lot of time and effort, particularly since I'm not an effects expert, but I look at it as a positive learning experience. The distortion is the only real weak spot, but again it might be because I'm using a single coil guitar (though I doubt that's the entire reason).
This one I'm not sure about. The first one I bought broke down on me, and I had to send it back twice in order to get it fixed. However, this was because the problem with mine was something unusual having to do with the circuit board and the technicians weren't used to dealing with that particular defect. That being said, however, it did take quite some time to get my machine back on both occasions, due to the fact that the techies had a lot of other SGXs to look at, so take that as you will. Since then no problems whatsoever. I'd give them the benefit of the doubt and say it's probably about as sturdy as most other rack mount equipment, but as with any RMequip. I'd take a few pedals along as backup to any gigs.
This is a good processor for people who like to play a little bit of everything, though I can't imagine it being ideal for someone who specializes in only one type of music. The main weakness is by far the distortion, which just doesn't get that heavy without sounding muddy. This shouldn't matter too much unless you play metal, which I happen to specialize in. Even alternative can stand the muddiness of the distortion settings, and the unit seems geared to that crowd. It does have input/output loops, though, so I'll probably build a collection of spare pedals with the SGX as my core machine (starting with distortion of course). Points off also for the unimaginative preset programming, with a good 3/4 of them being completely useless without some tweaking of your own. If and when I have to replace it, I'll probably spend a little extra and try a different processor, though I'm not really sorry I bought this one.