The point of a "pistol" lower is that it was the box checked on the form when it went thru the hands of the FFL. That seems to be the best way to avoid the entire SBR issue. You can have a pistol with almost any barrel length, but exceptions exist.
A rifle with stock is an SBR when the barrel is less than 16". In the specifics of this case, if the box checked was a "rifle" lower, someone could possibly make a case about it. Goes to just where and why the item was involved in a complaint, if the buffer tube could take a stock, etc. It's usually a lot more scary on the internet than in practice.
With the BATF making the SIG wrist brace legal, a lot of guys are now building "pistol" lowers and avoiding the $200 fee and paper.
Anyone producing eotech or aimpoint quality for less money?
Quite arguable. Case in point, the civilian models have parts made in the same plant in China as many others openly marked Made In China. You get what you pay for. One criteria to keep in mind is that neither have bulletproof glass or can be dropped off the back of a 5 ton truck with impunity. The light equipment companies servicing firearms in SW Asia have conexes full of optics damaged in use. It happens, and being "high quality" has nothing to do with it. A $200 red dot or $600, beat on it and it will fail.
Nonetheless, to a certain degree, you get what you pay for, of course. What usually happens in this discussion is that the "milspec" only users talk like anything less is a cheap NcStar, and the lower end guys sing the praises of $80 red dots based on Customer Service - they keep getting free ones.
I think a lot of us are inbetween - we'd like a good one with the long term low probability of it ever failing. That is the $200 -$400 class, which is the lower end of Aimpoint with the PRO.
There are dozens of threads here, on other forums, on the net, etc all detailing exactly why one red dot is better than another. Since there are so many on the market, it usually only gets the recommendation of the constant forum surfer who snags a chance to pump his favorite. Very few have owned and extensively used the dozen or so that might fit your needs.
One feature the milspec versions have is not seeing the red dot out the front lens. Not a good idea to have a dancing target right where the other guy needs to know where to shoot, especially at night. For use on a one way range or hunting, tho, it's paying for something you don't need. Second, waterproofness is very nice, nobody wants a foggy red dot, and it shouldn't even be questionable in the specs. If it is, they put it right out there. Third, what battery power is nice to know, some use expensive "tacticool" batteries that plump up the profile, others expensive button cells, and now we can get simple AA or AAA battery power. With those dirt cheap and common, there's almost no point whether the thing can stay on for five years or not. If it sits in the closet six months and you have a concern, swap in a newer one and go shoot.
Another item is whether the mount is part of the deal or not, spending another $30 to $100 on a riser needs to be included in the cost. It can make that $400 PRO a $500 installed sight - for some, a budget buster compared to another with the riser built in. Some might complain a integral riser is cheap, what it does is eliminate cost and having more screws to come loose, both are better.
Much after that is considered, then you get into what color dot, alternate reticles, and how it sights in with big knobs or just caps to keep from hanging up on stuff. Dpn't forget field of view, some of these are pretty small and htat means getting them aligned more closely. A pistol/SBR isn't a high precision gun, isn't long range, so the use of a scope with power isn't needed.
Best thing to do is plan a trip to a big enough gun store, Cabela's, etc and look thru them. Hands on tells you a lot more than what the internet can. What you like is different than ten guys dogpiling on an internet thread.
