If you need a glass beaded screen then it could be a good purchase. Personally I think it's a case of "caveat emptor" - buyer beware. I'm a bit concerned that the seller thinks that a projector with 1,000 - 2,000 ANSI lumens needs a glass beaded screen. I wouldn't supply or use a glass beaded screen on a pj with more than a few hundred. With that level of brightness hitting such a screen the only outcome will probably be hot spots and sparklies. Maybe they should include a pair of welding goggles rather than a projector mount. Clearly the seller knows more about gemstones than projection screens.
I'm using an AX100 with a glass beaded screen (GW II). The AX100 is considered to be one of the brightest projectors in its class, I have had no such problems with sparklies etc. PQ is also top drawer.
Not a good idea to paint electric screens, particulary if they're glass beaded. The resulting mess will be awful but no doubt somebody will make you consider it by saying that they did it and it was OK.
If you're using the projector and screen in sensible lighting levels, i.e. a dark and non reflective environment, then eco mode and a gain of 1 will be ideal. You will get a nice wide viewing angle and the colours will be as the projector manufacturer intended. More importantly, they'll be like that until the lamp has all but expired.
As the screen is the last item in the chain before the image reaches your eyes then it's worth spending a reasonable amount on making sure that you get the best out of it. After all you wouldn't buy a decent amplifier and stick car door speakers on because they were cheap.