The kit itself is impressive—which is to be expected at this price point. It comes with the gun, four standard capacity magazines with the factory extended base plates, four palm swells ("large," "medium large," "medium," and "small"), a kit with seven optic plates and five pairs of different screws, an "accessories" kit (pin tool and sleeker mag release), instructions, gun lock, etc.
The optics base plates and screws that come with it can be run with the following: Trijicon RMR, Leupold Delta Point, J-Point, Crimson Trace 1500, Docter, C-More STS, Insight MRDS, Leupold Delta Point Pro, and Nikon Spur. I'd note that the included base plates are plastic, so I imagine anyone using this for actual racing will want to upgrade the plate.
I'm not sure about holster compatibility ... I'm sure I still have my old M&P 1.0 holster around and I'm hoping that it'll work.
Build quality is good. The gun was dripping with oil, but I guess that's to be expected with a metal frame pistol, and I imagine it'll shake itself out after a few rounds. The mag well is removable and you can fit a sleeker mag release on it, in case you decide that you want to carry this gun as a slightly sleeker package.