I am interested in using a top rail adapter for semiauto 9mm.  (see the attached example)  We would like to have the option of using a reflex sight with a standard service type auto (Glock 17, Walther PPQ).

Does anyone have experience with these sort of adapters?  Are they reliable, safe and keep the zero intact?

 

For a Glock - the ALG Six Secound Mount is the answer.

https://algdefense.com/6-second-mount.html

There are even a couple of really good holster makers making rigs for these set ups.

I had the adapter from your photo, it did not hold zero between shots on an m&p_9pro.  I tried another where the open split was on the top rail, worked better. The problem is the dot is very high over the slide. I then switched to a dovetail mount, they are much much better (I think that was from speed shooter specialties, I still have it but it’s for an m&p). I found I liked shooting open so I had my slide carved to imbed the Trijicon. 

Also check out Carver, they make some better mounts as well. I have their comp/kkm setup.  https://www.bb-enterprise.biz/