I have three. All have been SBR'd.

1) Wiselite Sterling. Conversion done by KGB in Pompano Beach. Indistinguishable from factory. Fun to shoot,but awkward with the side-mount magazine.

2) CZ Scorpion. A blast. Easy to put a dot on with the top rail. Cheap magazines, functions wonderfully.

3) HK SP5. Got the stamp back today. MP5's are a blast to shoot, so I'm hoping that they're almost as much fun in semi-auto. Magazines are pricey.

Not a big company, but I've been more than satisfied with my 9mm AR design that was built for me by Battle Tested Equipment (BTE) here in Arizona. Originally it was purchased as a "handgun with a brace", but I went through ATFE to convert it as an SBR. The price was very reasonable, it's proven to be extremely reliable, accurate, and easy to maintain. Mine uses H&K MP5 magazines, but BTW can also build yours to utilize Glock magazines. 9mm was my choice, but you can have one made in .357 Sig, .40 S&W, or 10mm.

My other 9mm PCC is a B&T GHM9 Compact. Very nice, but more expensive as an initial purchase and the accessories aren't inexpensive either. I'm having this SBR'd now. Hopefully, my stamp will arrive in the not too distant future.

https://bte-usa.com/

I have both the Ruger and the CZ Evo. Both are great. I like shooting the CZ better. 30 round magazines are in the $20 are, so not outrageous.