Well for starters, just the setup instructions. The beer gun has a great manual with photos that clearly explains how it goes together and is to be used. Phill's philler is a photocopied page that was hard to read, all text and written (IMHO) rather complex instructions.
I found Phill's philler complicated. It needs two hands, better yet, three...two to work the levers (one lever opens/closes for vent release, one purges the bottle and floods it with C02- open/close and a third opens/closes for filling with beer) and one to hold the bottle. The apparatus requires you to insert it's wand into the bottle up to the stopper to get a good seal. I found this alone made the bottle too top heavy and was awkward without another set of hands. I wanted someone to steady the bottle while I worked the levers, swore, cleaned up and tried again.
The Beer Gun is a stainless steel, one handed (well, two if you count the hand holding the bottle) über gadget! Insert wand. Push button to flood with C02 - release. Pull trigger to start flow of beer - release. Pull out wand and cap. Done. Simple. Well worth the money.
Go buy one and send me $5 for making your life easier!

If anyone's interested, I'll bring it to our next meeting and folks can see it first hand (well, not in use).