I have built two 19's, one 17, and one 43 using JSD Supply. The only issue I have had was with the 43.
After about 300 rounds the 43 would do something weird. I'd pull the trigger and the first or second round would functioned properly. The third round it would eject the spent brass, eject a cartridge, and then shoot again. It would double tap with a cartridge in between. This was with 2Amend magazines.
I bought factory Glock mags and it stopped doing it. But, like I said, that was with about 300 through it.
The one 19 and the 17 are absolutely flawless. I've mag dumped them many times and slow methodical. They just run.
The second 19 I just completed last night. It has not been shot yet.
My favorite is an FN40 long slide. HKparts.net sells original FN kits for $399 and $27 shipping, but they come with all original parts, one 14 round mag, owner's manual, and hard case. It's a pretty good deal. I may buy another one of those.
FN40 long slide at HKpartsUS Patriot Armory has OEM Glock 19 kits, but they are $440.
OEM Glock 19 at Patriot Armory