Here are some references about those rifles
http://www.ar15.com/archive/topic.html?b=3&f=12&t=209756
http://www.ar15.com/archive/topic.html?b=3&f=118&t=315010
(May need account to access the AR15 archive server.)
http://demigodllc.com/articles/evolution-of-the-3-gun-practical-rifle/
There is no reason you have to have a muzzle brake on there - I just do for 3Gun. I've also used other muzzle devices:
The first one - the painted tan one - was built specifically to fulfill both the high-intensity and the carbine precision parts of the ITRC match, as well as being a great 3Gun/practical rifle. This meant it needed to be able to engage small targets to the limit to 223/556 as well as maintain reliability through high-intensity courses of fire, namely the 300 round in 15-30 minute section of the ITRC. So there were a number of reliability and zero-retention features we went for.
As you point out, it is very close to a practical/tactical configuration, there is not much to argue against other than perhaps the brake.
In any case, the basic configuration is fairly simple: 17", rifle length gas system, mid-light weight profile barrel (about 0.72" under handguards, 0.75" forward of gas block), PRI carbon fiber float tube with optional/selectable rail segments, pinned gas block (for reliability).
The lowers have Magpul stuff because I like it and I run JP 4# triggers on almost everything. These have been 100% reliable over tens of thousands of rounds and 7 years.
On the trigger guard, I actually like it more because it fills in that void right in front of the grip (the square hole where a "gapper" might go) and provides a little wider platform and a different angle of support, which I find helpful especially when manipulating the gun and holding it strong-hand only.
Anyway, what's interesting is that the last photo I posted is basically Rock River 16" MLGS, which just had the barrel turned down a bit to save on weight an a LaRue rail system added. It's been very reliable and would be a good choice for a general utility/fighting upper.