I owned one of these for about a year. It functioned perfectly, and I even shot it well enough to get a 2nd place finish in a local competition, the first time I shot a match with it. Ultimately, I decided to get rid of it for the following reasons:
- The full-time ambidextrous magazine release used on some of the SF Glock models has a history of problems. Although mine never broke, a lot of folks have experienced broken mag catch assemblies on the ambi SF models. If it breaks, Glock will replace your frame with a frame using a conventional mag release system, and I believe they have stopped making guns with the ambi system, which pretty much tells you everything you need to know about its long-term durability.
- If you have the full-time ambi release frame, to get spare mags you must find/buy the newest generation of magazines that have a rectangular cutout centered on the front edge of the mag body. Older G21 mags WILL NOT WORK with the full-time ambi mag release system. Even before the latest buying frenzy, it was often difficult to get mags, as some online retailers would advertise their Glock mags as the newest/latest generation, but if you bought some, often one or more of the mags would be an older version which would not work in the new ambi-release frame.
- The 21SF was the only large-frame Glock I owned; all the others were the smaller 9mm/.40 frame. A combination of the slightly different SF grip angle and the overall "chubbiness" of the .45 frame was messing-up my high-speed shooting with the other smaller-frame Glocks. This was bugging me, so the 21SF had to go.
- Price of .45 ACP ammo. 'nuff said.
The full-time ambi-release SF models are on the short list of Glocks I will NOT recommend, just because of the mag release and mag availability problems. Once modified to a standard release frame, of if you bought a SF with the standard-style-mag-release-frame at the beginning, then they are good-to-go.
"Placement is power" -- seen in an article by Stephen A. Camp
(RIP, Mr. Camp; you will be remembered, and missed)