I bought a 32C (.357 sig round) a little over a year and a half ago. I bought it when my department went to the 31, and it was the last 32 left (with a 2 month wait on any more to come - I work primarily plain clothes so smaller is better up to a point). I was concerned about all of the rumors I had heard about muzzle flash and whatnot, but decided to try it on the advice of my then-SWAT team commander, who had a comped Glock (and this guy is a pretty good firearms instructor and tac guy).
My partner bought the last 32 out from under me (the bastard), so I have gotten to shoot them side by side. Here's what I have found:
-Muzzle flash problems - basically, when shooting at night or low-light conditions, the shape of the flash blindness left in your eyes is a different. You are equally blind with both guns after firing. With good ammo, it's not a huge deal, but you should be carrying a light anyway. Don't worry about it, and get a white light. Train with it. Problem solved.
-Port Blast - figured this out the first day I had it. Did out PD qual, which starts out with a QCB/weapons retention position very close in to the body at close range. The ports create a little pressure that you notice a little on the range. It is not painful or debilitating in any way. Again - about the same as the non-comped gun. If you stick your eyeball on the port, you will have problems. If you stick your eyeball on the muzzle, you will have problems. Keep your eyeballs more than a foot from where the fire comes out of the gun, and you will have no problems. Don't stick your tongue in the ports either. Again, problem solved.
-Getting Burned - i'll light my left arm on fire if it means I will win the gunfight. Worry about getting shot, not about boo-boos. Don't get into gunfights while covered in gasoline, and you should be OK.
-velocity loss - it was about 15 fps compared to my partner's 32. I have shot this gun into ballistic gel at a terminal ballistics workshop, and it performed every bit as well with the same ammo as the 32 and 21 (penetration depth and expansion of bullet). I have one of the bullets I saved around here somewhere. BTW, we use Speer Gold Dot 125 grainers.
Now, the ports really do reduce the muzzle flip, and I shoot better with this gun than any other I have ever had (493/500 was what I shot the first time I qualled with it on a 50 shot, 1-50 yard timed course). If you are not accurate with your 23, the 23c won't help. Practice will - the c helps control muzzle flip only, and might help you with a flinch if that's your problem. If you are wanting the comp to solve your accuracy problems, you are barking up the wrong tree. If you want it to help your shot to shot recovery time, this can help.
Comped Glocks are viable defense tools. Do not discount them. The 'problems' are insignificant relative to whatever you are facing in your gunfight, if it happens.
Just my $0.02 - but it is based on actual experience with both types of guns.