Chuck, you are absolutely spot on with the consistency issue. If its not consistent it really is a waste. Which leads into what koon said, bottles are a big waste, more expensive, a pain in the ass to lug around, and you have to go to a specialty store for refills. You can get propane tanks filled and/or exchanged at so many different locations at any time of day. a good co2 generator is much more consistent at keeping ppms in range and it cost me less than $7 a month in propane to supply both of my rooms with co2.