Powertank is a CO2 system. Co2 stored at high pressure with a regulator tailored to the hobby. I have used them for years wheeling and I can usually fill my (4) 37" Toyo's from 8-10psi aired down to my running pressure of 27psi about 6 times before I need a refill on a 10# tank. I have the Monster valves which make airing down all 4 tires very fast, maybe a minute for all 4. Airing up with the power tank and monster valves takes about 25 seconds each corner. Setting beads and running air tools are great withth is set-up.
I also run a single ARB pump mounted under hood, which I use for ARB locker and for airing up when I'm not in a hurry to save on CO2 (when there is beer in the cooler).
In my opinion, if you can afford a power tank and a small compressor, you are FAR ahead of where you would be with a compressor and tank. You have redundancy and FAR superior pressures to work with when needed. There are a million places to have the tank filled, but if you are moving fast on a long distance haul, having to wait a day for a refill could be a pain. But for a week trip or so, I cant imagine you would need to refill the tank....