Going with an small, oddball size CO2 tank is a compromise of compact over convenience.
Standard 20 lb. CO2 tanks are a quick and easy exchange at industrial gas suppliers versus having your Powertank 5 or 10 lb. filled while you wait.
I built my own CO2 air-up system using a 20 lb. CO2 tank for a fraction of the cost of buying a Powertank, etc. The 20lb. CO2 bottle can air-up a lot of 33 inch off-road tires before needing to be refilled. And I normally carry it in a FJ40 Land Cruiser, so it is not "too big."
My US $00.02
Alan
I priced out the the individual parts vs the Powertank package, and did not find significant savings. Perhaps I did not find the best vendors, and maybe could have found less expensive options. At any rate, I did opt for the convenience of a complete package.
10lbs will easily last me 2-3 months, summer aside (when it is too hot to regularly go out). I estimate 2 or 3 recharges a year. It is okay.
Vendors and turn-key packages aside, I am very pleased with the C02 solution as a whole.
I was able to reseat a bead with no fuss or issue. I did a test run in my garage, by breaking the bead on my spare.
And not having to mess around with an air compressor in 100 heat for ~20 minutes after a trail run, priceless.