ATF = Automatic Transmission Fluid.
Brownells used to sell MPro7, not sure if they still do.
Gunscrubber would be fine for use on your upper, just make sure you have it detached from your lower, and that you properly lube everything afterwards to prevent oxidation. I agree that it probably isn't a good idea to use it on your lower/FCG.
Breakfree will work in all three roles mentioned, but it works best as a protectant, with lubrication and cleaning taking a back seat somewhat. A lot of people are switching over to FP-10 from breakfree because it is a better cleaner and lube, especially a better lube. Still, Breakfree is a much better lube then straight up mineral/3in1/motor oil, in my opinion. For me, the jury is still out on wheather FP-10 is a better protectant than Breakfree, there is a lot of empirical evidence that suggests Breakfree is an awesome protectant against corrosion.
It should be said that Hoppe's, MPro7, or any other nitro and/or copper solvent will remove fouling easier and faster than Breakfree or FP-10 CLP. The downside is that the solvents only work as solvents, and they may be a bit more reactive. General rule is that you don't mix solvents since that can create new compounds that may be corrosive or eat steel and aluminum. Hoppes No. 9 is a good, low-reactive solvent that does a good job at removing carbon but not copper.
Everyone has there own system for cleaning things. Personally, I use Hoppe's to clean the bore (use a copper solvent maybe once a year to remove any copper buildup) and use either Breakfree or FP-10 to loosen up the carbon on the bolt/carrier and to clean the inside of the upper receiver. Will then use Gun scrubber or brake cleaner to wash off all the loosened up gunk on the bolt and carrier. Re-lube with CLP and call it good. Don't bother cleaning the lower and FCG since those parts never get fouled.