I would avoid the Serpa if for no other reason than that they are getting banned at lots of training facilities and by lots of big name trainers, so if you go get yourself some pro instruction, there's a decent chance you'd have to replace it anyway.
There are other reasons I would avoid it as well, although I do think the degree to which they are seen to be ticking time bombs has been exaggerated. Mainly, they're cheap, poorly built, and have effectively placed the "landing gear down" lever next to the "shut engines off mid-flight" lever. Can you work around it? Sure. Would I rather fly a plane with those levers on opposite sides of the cockpit? For obvious reasons, yes.
If you MUST have L2 retention, go with the Safariland ALS. Much better quality holster.
Otherwise there are a lot of companies doing the kydex pancake thing. Raven as mentioned above, plus a nearly endless list...Kaluban Cloak, Atomic Dog, Cane and Derby, the list just goes on and on now. Peters Spada. I think DeSantis makes one now. Personal Security Systems. I'm just naming them as they pop in to my head. There are a zillion makers. I use the Atomic Dog stuff myself...very heavy duty, nice stuff.
Also Praetor Defense is making a lot of waves right now...for a G17 with no light, pretty good way to go.