I was asked to build a 10.5" barreled 5.56mm AR pistol for someone and when I tested it, it was the loudest rifle I have ever shot and it ripped a long flame too. I was wearing ear plugs with ear phones over the top and firing that gun still made my ears ring. I would not want to shoot it inside a closed in space, like my home. Personally, I like .300 BLK subs for SD in the home. I have a nice little 8.5" barrel .300BLK AR pistol setup for subs and without a suppressor it is still much quieter than a .22LR. BTW, if you get an AR Pistol in .300BLK make sure you get the pistol length gas. And anything with a short barrel, I would advise using a flash can. It is too easy to lose a finger with a birdcage or other comp. The flash can directs everything forward, including most of the noise.
Personally, ARs are at the point that brand names are pretty much meaningless and if you can put Legos together, you can build an AR. Kits in a number of forms are pretty cheap. The only thing that is required to go through a FFL is the lower receiver.
Now as far as braces, I like the ShockWave with their KAK buffer tube. The tube has set points that will allow you to lock the ShockWave into position with its set screw without harming the tube. I have an early model Sig and it is heavy and only has one position (short). I have not tried the newer SB braces, but the cost is high IMO. None of the AR pistols I have shot have enough recoil to make the ShockWave uncomfortable, even with extended shooting.
I haven't seen anyone talking about it here, but PCC ARs are now developed to the point where you can build a reliable weapon from parts. I have 2 AR9s, one that uses Colt 9mm mags and the other uses Glock mags. The Colt mags one locks back after the last round, and the Glock one does not, sort of like the difference between a AR and an AK. They both work, just a little different. Also, if you have any aspirations of getting a suppressor, get a handguard with 1.5" ID. I usually get my hand guard a little longer than my barrel so that 3" flash can only peeks out an inch or two. With a 1.5" inside diameter HG your suppressor can connect under the HG and look more finished. I have a 9" hand guard on one of my AR9s with a 7.5" barrel, so the flash can sticks out about 1.5" and has a very intimidating look.
While I am thinking about suppressors, don't get a quick connect, it really is a waste of money. Every time you remove the suppressor and remount it, it will require being rezero'd, that includes when you remove it for cleaning. Also, most suppressors have varying degrees of blow back. If you are a lefty, like me, that means it will hit you in the face and on the right arm. There are a couple of designs that eliminate blow back and there are also a few over the barrel designs that essentially shorten the length of your gun with a suppressor mounted.