I bought one about 6 months ago.
It's a great toy, and does a good job filling bottles.
One thing to remember is the 10' of tubing is at room temperature. You can see "backflow" of bubbles (CO2) in the tubing. If you could keep this ice cold, you would not have to purge the gun before each filling.
I sanitize my bottles (Iodophor), take CO2 to displace the Iodophor, then put a 2" x 2" aluminum foil cap on the bottle.
Even with purging, I use the beer gun's purge feature. Guess I'm REALLY paranoid about staling beer.
No matter how fast I go, I always have to purge the line before clear beer will flow through the gun.
I do have to reduce the pressure to avoid foaming.
NEVER, NEVER change the pressure on your CO2 cylinder once you are happy with the fills. This changes everything (been there, have the hat and t-shirt). I think this is something very basic and maybe I'm a doofus, but have not seen this statement made before). Once you are keyed in, just keep filling at the same pressure.
It's a great toy (oops, meant tool). I think it's worth the money.