If you want the vest, get it. Your always going to get nay sayers no matter what you do. If your willing to put up with and deal with the down sides, what do they care, your the one who has to wear it. This kind of reminds me of all the posts telling you you cant carry full sized pistols all day, everyday without everyone knowing, or you dying from the weight and size, etc, because "they" cant for some reason.
Personally, I'd wear the vest and carry a gun if I was working the graveyard shift at the local UniMart.
Yes, they can be hot, especially outside in the summer and warmer months or if your stuck inside in the heat all day in the winter. Your fitness and activity level will also have a big bearing on your comfort. Overweight and inactive people seem to have enough problems just sitting still in the A/C. If your fit or fat, your experiences may be somewhat different.
The "hot" issue is actually a benefit when outside in colder weather, and sometimes at the indoor ranges in the winter as they usually have the heat off and fans on. They are somewhat restrictive, and if you carry IWB, can sometimes interfere and pinch you if you move the wrong way. Theres no doubt, they can be annoying.
They do have their uses though. I have a couple and they get used a fair bit, and especially from this point on through winter. I always wear mine when ever I'm in the woods working/hunting during deer season(we work in the shotgun only zone), or at the range, and especially at the indoor ranges.
Most all the indoor (and outdoor for that matter) ranges I've been to are fairy well riddled with holes, and in just about all surfaces too. If I have to shoot around other people, then I always wear one. There are just to many knuckle heads out there these days and they seem to let anyone in if they show their money.