I have had most of the parts for this for a while, but I finally got around to putting it together and also found a good deal on another Nikon scope like I have on my other 300 Blackouts.
Main reason I ended up building this was I found a 16" AAC barrel in .300blk being clearanced on Numrich's website for a little over $100 (normally about a $400 barrel). Figured I would get it and eventually have it chopped back for my spare SBRed lower, but later I decided to build it at 16" instead. The parts are mostly Aero other than the AAC barrel, flash hider, and Daniel Defense stock. I may get an extended charging handle and a better trigger at some point if I find those items on sale. Probably not going to bother with BUIS due to the fixed scope mount and the fact that it's just a spare rifle.
Upper and lower are both their M4E1 series. The upper mounts the rail/handguard direct to the upper forging so you don't have to worry about timing of the barrel nut or anything like that, and if you are using a handguard with full rail on the top, you don't get that double wide spot between the slots like you usually see. Probably other features too. The lowers are nice because the trigger guard is part of the forging, so no roll pin there, and no roll pin for the bolt release either since it uses a special threaded pin. The pin comes with the lower but if you want a spare, buy Aero's LPK because there will be one in there, too. There's also the tension screw under the grip you can use to tighten up fit with the upper, which eliminates any need for a wedge.
Only reason I bought the DD stock was it has an overmolded cheek piece similar to the Hogue stock that I really like, but it also has a rotation limited sling swivel, which is a feature I think is important, and the Hogue doesn't have that. But having bought it, I don't really care for the DD stock. It works, and I don't plan to replace it, I just wouldn't buy another one. It's almost too tight on the buffer tube, and the recoil pad setup is borked.
I also can't recommend the Aero scope mount. I like most of Aero's stuff a lot, but because of the way the rings on this mount tighten, the scope will rotate clockwise as the screws are torqued. So you may think you have it level, but you really don't because it is going to rotate on you. You have to guess at how far counterclockwise out of level to start by trial and error. And if you're using a dab of blue loctite on the screws, you are racing against the cure time. Now that I have it in place I will leave it there, but if I ever have a reason to remove the scope I am probably going to replace the mount with something else that is less stupid.
My original plan had been to move the Nikon 1.5-6 scope and Bobro mount from my SBR to this rifle and get a different optic for the SBR, but then I found the same scope on sale for less than half price (still more than I paid for the first one) and now my blackouts all use the same scope and reticle. It's not really a "tactical" scope but it is good quality and has clear glass. Probably not worth the $700 MSRP but it's a good scope if you can find it on sale.
Went with their Quantum upper because I didn't really see the need for rail running all the way out, and it was less expensive. It does have a short section in the front for a BUIS that I am not going to add.