WRT using/training on a single type of platform, here are my thoughts:
In the training community, there’s a theory known as Hick’s law. The simplified version of that is that, for every choice you give an officer, the decision part of the OODA loop gets longer (by how much, we’ll never know, but it’s noticable). This is usually discussed in terms of non-lethals; e.g. given a combative subject and an officer armed with pistol, impact weapon, chemical weapon, and/or taser, he has to look at the threat and decide - “is this an open hand threat? No? Then should I use spray? No? Should I use the baton?..” You can probably see how this can lead to “death by analysis.”
I’m not sure the same law applies to using different types of handguns, at least among pistols that are generally as similar as the ones you’ve described. For decades, I’ve been a Glock guy primarily, unless forced by agency mandate to shoot something else. I have never, however, found myself in a situation where I couldn’t adequately operate a Sig, Beretta, or HK under stress.
Now, there are some platforms that are different. I’m a FIRM believer that if you’re going to carry a 1911, you should ONLY carry 1911s to limit the problems associated with safety manipulation and the VERY short, light trigger pull on that wonderful platform.
Likewise, through a series of unfortunate events, I’ve found myself without a Glock for the last four or five months; and, in the interim, I’ve been carrying my personally owned P7M8. Now, I’ve owned P7s for over 20 years now, and I’ve probably shot cumulatively well over 10K rounds through various P7s over the years. On the range, doing our non-challenging qual course, I’ve had no problem working the P7.
Fast forward to last Friday, when we were doing stress drills on the range. I’m not too proud to admit that at least twice in the early drills I simply forgot to “squeeze” the grip enough to cock the striker - and I was getting ready to tap-rack-bang before I realize the failure is in my grip…
So, while I think that it’s generally OK to have more than one type of gun in your carry stable (even when I did have a G19 that worked as a primary, my BUG was a Kahr PM9 or S&W 642), I’d recommend mixing in “unique” manual of arms guns.
Regards,
Kevin