The nice thing about an air tap in this instance is that drunken friends can pump the keg themselves, instead of fiddling about with those tiny CO2 cartridges. If the kegs are gonna kick in an afternoon/evening, and the brewer wants to have fun too, why insist he fanny about with all those cartridges? He'd be replacing one every fifteen minutes at that rate of pour. Plus there's all that metallic waste, not to mention his friends making fun of him for bringing whippets as well as beer.
I'd get the hand pump and have done. I do the same thing - I've got four Cornies with Hoff-Stevens fittings in the lid, and a hand-tap to go with it. Well, I've got CO2 push, too, but I'm confessing for the principle of the thing.
Tip: Make sure there's a check valve in the air-in line. If it's a loose, hand-held pump, all you need is a drunken idiot flailing away at the pump and pulling it off the line or keg - then all your pressurized beer will come out the air-in line. Funny on video, but heartbreaking.