Shadow Systems has an excellent setup and their pistols shoot extremely well (feels a tad bit flatter vs an oem glock to me).
I own a few MR920s and the biggest downside is mounting a closed emitter. This can be remedied by getting a non OR model and getting it cut or running a G19 slide. I prefer a direct cut 509T as my optic and the G19 slide on shadow systems frame has run really well for me. My main training gun is on around 16k rounds with this combo.