That is something Salient offers, but I learned about after having one for a while.
GTG out of the box you say, eh?
Yup, my other concern was the flat top for the RDS, like the 1st gen Walther PDP's. But Shadow uses way longer screws and uses a buffer type insert between the slide and optic which minimizes the side to side, and back and forth travel of the RDS. So seems like they mitigated that issue. Their slide is designed to take longer screws, compared to a Glock slide that's milled.
But yeah, I could buy a G19, then upgrade the slide to look tacticool, buy a tacticool barrel, Holosun RDS, stippple, etc... Or just buy the MR920 and ready. I haven't looked into it yet, but it should fit G19 holsters and accept G19 mags (Glock factory mags).
Mrs. CMO not happy about me buying 2 pistols so close together. But my excuse is I didn't pay for the M45 yet, so technically, I didn't.