MOS vs CORE (vs Custom)
The Glock MOS and the CORE are both manufacturers' attempts to make a generic slide cut to take a variety of optics. As such, they compromise the real, proper mounting of a Red Dot Sight (RDS) on a pistol slide.
The proper way to do this is to choose a good optic and have your slide milled specifically for that optic and install suppressor height sights to co-witness through the RDS.
The MOS has a relatively thick mounting plate adapter that raises most RDS too high above the slide. The RDS can only be mounted to this plate, which although thick, is not thick enough for RDS mounting screws to get a full purchase. Sights have flown off the Glocks, and the OEM MOS iron sights sit too low to cowitness properly through the elevated RDS. You will need to buy taller aftermarket Glock sights to get the system to work properly, and then you still have a weakened compromise.
S&W did a better job with the CORE, as the RDS mounting is more secure and lower. It comes with taller sights. However, it's still a generic compromise. If you want to go cheap, with an inexpensive RDS, the CORE will probably give you better performance for less money in the long run. However, one of the best optics, the Delta Point Pro, will not fit on a CORE.
Many people prefer the ergonomics of the M&P. Stock triggers are generally a little better with the CORE than the MOS.
Both guns can be customized with triggers and other mods, but in my mind you're throwing good money into comparatively substandard systems.
That is my opinion, not backed up with personal experience with either a MOS or CORE. I read of the weaknesses of these two systems, so I went with a custom milled slide on my FS M&P and a Trijicon RMR 06. I spent a little more up front, and I have added other enhancements to make this pistol a real good shooter. I am pleased with it in all respects.
However, I am not a competitor like some of the real experienced guys on this board. I get schooled regularly here by the people who have really BTDT.
In my decision making, money is a fourth tier factor, after performance, reliability, ease of use. I have paid my dues in past decades with doing things on the cheap and can now afford to do them right. That is not the case for everyone, so your decisions must be based on your priorities.
I'm not trying to piss anyone else off for their choices, but some fail to explore all the options before they pop for the heavily marketed manufactured compromises.
