For my Glock 19 SBR:
RONI: steer far clear -> I've had lots of fit problems which impede function. With slide contact, with getting a silencer on, fit and finish, randomly falling apart, etc.
Hera arms conversion: meh, it works. I never use it.
Fab Defense and B&T kits both look cool, and I guess I SBR'd a Glock, so I might as well try to find something good for it. Honestly, my comment over 10 years ago (!) on this forum to steer clear of SBR-ing a Glock was probably right. Almost exactly 10 years later I did one, and I really haven't found a sweet spot for it yet.
In terms of more PCC/PDW type setups, the CZ Scorpion is awesome all day long, MP5 and MPX yada yada (I know I'm supposed to like the MP5 and MPX more, but I personally prefer the Scorpion out at the range -- $50-100 in HB Industries parts and it performs like a dream, mags are cheap and synthetic, etc), micro-Draco for com-bloc SBR, etc.