UPDATE:
I'm loving this stuff and find myself using it everywhere. I installed new doors in our house and before installing the knobs and dead bolts I sprayed them with FF and they are super smooth. I've coated my metal shaping tools with a thin film, sprayed it on my folding bike rack, trailer receiver, and the camper stabilizer legs and receiver. Everything operates smoother and any rust has stopped.
I've used FF on my Glocks and CZ as a rust proofer and lubricant on my barrels, rails and I'm really impressed. I just put a very thin coating on my barrels and it does not dry out and the slides feel smooth. I would say its just as smooth as anything else I've tried. I like using it on the outside of the slide by buffing FF into the finish and it leaves a nice sheen that doesn't dry out. I went shooting with the G21 and P07 and the spent powder wiped off the slide and barrel. When I cleaned the barrels I sprayed FF down in the barrel and let it soak in while I cleaned the rest of the gun. Then I used a barrel brush to scrub the bore and finished it off my running a bore snake through them. The bores looked great and I feel the light film will keep them protected while not over-lubing them. I keep a microfiber cloth in my bedroom to wipe the pistols down as I handle/carry them and there is enough residual FF in the rag that it acts like a silicone impregnated rag. I don't have to spray FF directly on the slides every time before I wipe them down for storage in the safe. Its fast, clean and easy to touch up the guns for storage.
Here are pictures of the sheet metal lubed and clean before it was put out in the elements, and also outside. It has been sitting outside for a couple of weeks but we just got rain last night. Until last night they were all looking rust free although the BC synthetic gun oil had some faint surface rust forming. It probably would have just wiped off it was so minor but rust is rust.
Last nights hard rain is what really put the oils to the test and FF came out on top. The sheet metal was sitting face up and rain collected on it but you can see the major rust that developed overnight. Both FF section are absolutely rust free.
The metal piece I used was an older piece that was sitting in the garage so it had some stains from storage prior to the this test. I think you'll be able to see what stains existed before the test and which rust is new.
Before the elements (stained but clean and free of other oils not used in the test)
After being outside for 2 weeks and last nights rain collecting on it. (The FF sprayed section has bugs and debris stuck to it but its rust free. The FF section that was wiped on with a microfiber cloth is clean of debris and rust free.)
I can't wait to spray the underside of my new vehicle before winter. It should provide good protection against salt, water and sand. Its supposed to rain off and on for the next week so I'll continue this test for as long as I can; probably through winter also. I'll keep doing updates as well.