I really like that beer gun, but I have 2 questions:
1, I will still need to siphon the beer into a bucket with priming sugar, right?
Beer guns are designed to bottle from a carbonated keg and purge with CO2 before filling. So, the priming sugar, should you choose to use it, would go in the keg. Since you need CO2 to push the beer anyway, I would artificially carb.
That being said, a single filler followed by a bench capper is an excellent method to speed it up. The concept is to make an assembly line with the least number of movements. With two people well versed in the process, I used to be able to bottle 10 gallons in identical height 12 oz bottles including sanitizing the bottles in about 30-45 minutes (not including boiling the priming sugar and transferring to the bottling bucket).
The entire kit was two bottle sanitizers shoulder width apart on top of two 6 prong bottle trees. This assembly spins so that the six oldest bottles are always adjacent the filling stand.
Next was the 3/8" ID filler hard mounted about 18" from the bottle trees and 18" from the bench capper. A foot pedal raised the bottle to the filler.
The capper was mounted to a "runner" of Formica so that the freshly filled bottle was slid to a stop, cap into the magnetic bell, pull and place in case.
One person ran both the filler and capper as it took about the same time to fill a bottle as it did to load the capper, cap and place the capped bottle in the case. The other person was busy sanitizing bottles, clearing filled cases and generally tending to the one doing the filling.
Everything but the capper and the bottle sanitizers was junk fabbed together from my garage. I used to have so much more free time. I sold it to member of my homebrew club back in OK when I moved to kegging.