Does anyone have prolonged experience with these? I have a 1st gen shield for summertime carry that I'd like to up the capacity on without using extended mags (yes I'm aware these extend the magazine 1/4 of an inch) and defeating the purpose of using the shield. I also don't want to deal with the hassle of trying to sell it and buying a shield plus or something else.

My concern is reliability, obviously. I want to hear from people who have used these for a while and not just "they worked fine when I tried them at the range". High round counts, dirty, etc.

I put a Magguts LCP +1 in my P3AT and it ran 100% with every type of mixed hollowpoint I ran through it!  10,000 flawless rounds!

Just kidding.  It choked on plain old American Eagle ball.

I have had MagGuts kits in multiple G42 and P365 mags.  Both pistols/mags are carry guns.  

I don't have an exact round count through each mag, but I’d guess about several hundred rounds minimum per each mag with the MagGuts conversion.

I’ve never had an issue with any of the Mag Guts equipped magazines.

100% reliable with OEM 10, 13, and 15 rounders
https://www.gunbroker.com/item/986690365
$100 + trsf, tax

(about the same price as 3 of the MG conversion kits)
I did the MG thing and they did ok the one time I tested them.
I just prefer OEM over aftermarket.

I use the Magguts on some of my Walther PPS mags and also Ruger LCP. No problems with them.