I called him out on it, because for a while there (somewhere in the `09 period before I found this place IIRC) he was letting his reputation exceed him.
I don't think Rob's a bad guy, and with the attention that spreadsheet got him, I can't really fault him for playing it up on the interwebs either. It definitely grew legs and ran away from him. At the end of the day, he's been through several gun courses (advanced training), and he'd wipe the range with me score wise if we were to go MvM, but he's not an operator and he openly admits that. I'm not either, and I openly admit that too.
Now to throw my .02 into the ring on the subject: I stick with Mil-spec parts for one simple reason - tolerance compatibility and material qualifications. No more, no less.
Mil-spec materials were chosen for performance/reliability/durability, and as such I choose to go with those because the Military feels they're acceptable in service for a long time with minimal maintenance. The 1989 FN M16A2 I had in BCT might not have had any original parts attached to it for all I know - but the package I was handed was a very well functioning rifle, and I can assure you no one hand fitted a damn thing on that gun.
I do get my undies in a bunch over billet this and forged that - but mainly because I hate when people misrepresent what the two processes really are and how they impact the ultimate finished product. A 6061-T6 "billet" (should be called "bar stock") receiver will function as a gun just as reliably as a properly forged 7075-T6 mil-spec, with the possible exception of having poorer wear properties, since 6061 is a softer material with less silicon in it. I've said a few times over the years, that 7075 is not chosen because it's required for the gun to function as a gun - it's chosen because the gun is designed to function as a club, and sustain falling out of helicopters without breaking or bending to the point it's not functional. If you have no desire to to buttstroke someone to the head or affix bayonetts to your ar15, you probably wouldn't notice your 6061 upper, lower, or buffer tube wasn't as strong as a 7075 forged one. After 20,000 rounds (arbitrary number), you might start seeing some additional wear on the contact surfaces though.
Dimensional accuracy to spec: To ensure interchangeability, the parts need to be held to the allowable tolerance on the blueprints. Anyone can change those dimensions and as long as their other parts are also changed to remain compatible, there's no problem (the commercial buttstock is a prime example of this), so I stick with the military's print for all my parts. This ensures that not only will the gun function when I assemble it, but if I have to rob parts off another one to regain function after a failure, those parts will also work without modification. I have no love or time for proprietary components on a gun that might need to save my ass some day. I want to be able to swap a bolt out, or hammer spring, or upper, and not wonder if it's going to work. This is a sticky issue with the AR10's, as they have so many variations between manufacturers that it's often a crap shoot if your gun will work without knowing what flavor the parts are. Apple computers used to be the same way (proprietary parts you had to get from them), and I still have no love for them because of it.
The AR/M16 bolt carrier issue is kinda moot here, and more valid in states like AZ. I don't envision MN allowing civilian new manufacture automatic weapons in my lifetime, so the ability to trigger the auto sear isn't much of an argument (the lower needs to be milled out and another hole added for that to fit anyway). The additional carrier weight for a carbine is valid, in a rifle not so much. The situation can be corrected with an extra heavy buffer, so it's not a deal breaker (for me) either way. If you look at the bottom of a mil-spec upper, you can see where there's an oval machined out just in front the rear pin tab - that's the upper side of the full auto sear pocket.
At the end of the day, you need to be able to trust the weapon you have if you're using it as a defensive gun. You can get that trust from buying known brands, or you can shoot the ever love'n piss out of the thing til you're sure it's going to work. I tend to use both methods, as even a known brand can (and will) break from time to time.