I'd agree... I built one of these over the last couple of months, according to that schematic I re-posted. Finally got around to trying it last night, to empty my kegs so I can redesign my Pleaser-Keezer. Anyway, I agree with TheCrowsNest about 'a little messy' but by the 4th bottle, I had a routine:
(1) With one hand, hold the picnic-tap head (pipe wedged into it) while pushing the stopper down into the bottle
(2) with the other hand, push the tire valve release slowly to let the pressure out of the bottle so the beer-level slowly rose-up without foaming.
(3) use one hand to steady the bottle and the other to pull the stopper loose
(4) swished a cap in some sanitizing solution, placed it on top of the bottle
(5) pressed the cap down with my thumb and turned the bottle over twice to start it foaming a bit
(6) just as the foam started to push the cap up, I capped the bottle
During the first 1-3 attempts, I was absolutely convinced to buy a beer-gun but like I said, by the 4th, I was glad I hadn't given-up. (the first 3 just had too much head-space because they got a bit foamy and I panicked and capped them too soon)
Maybe I'll get inspired and post a video on YouTube