My experience with these for gaming is limited. I do own a pair of these, which have a primary duty of my main development monitors in my home office. Just last weekend, I hooked up the system that will eventually get housed in my upcoming cabinet build to one of them. The response time is good, and the black contrast ratio is outstanding. In general, everything I run is dark themed, from my OS to Visual Studio. It is the sort of build quality that I expect from ASUS, overall.
As for my testing, I did run at native resolution for a while, and the stretching was noticeable, but not to the point it was distracting. By comparison, I have a 32" Ultrawide LG that I use for a workbench machine, as it has multiple inputs. If I run on that, it is comical (because of the 21:9 aspect ratio). However, on the ASUS, I did spend some time playing with it forced to a 4:3 through ATI Catalyst, and you do not lose as much space as you might think you would, should you decide to try something similar, at some point.
For me, pros outweigh the cons - mainly because I do not have any cons for this monitor (apart from the fact that I wish I had the room on my desk for a pair of the 27" ones, and that it is a fraction of what I paid for mine). I've left both of mine on 24/7 since I've purchased them, and there are no adverse effects to it. Between the two that I have and the two that my wife has, no dead pixels, no artifacting, and the color is pretty consistent between all four of them. Whether for a cabinet or general computing use, I would not hesitate on them, should I be in the market for monitors.