I have a 4x4 gorilla tent running CO2 with a 26 lb bottle and it lasts about 4 weeks. ( definitely get a controller.)
I can say without a doubt, it is the single biggest thing I changed this grow and it most definitely works.
I tried exhale grow bags but now looking back if had to do it again I wouldn’t hesitate to get a proper cO2 setup.
I am simply mesmerized by the effect it had. It’s ok, I wasn’t a believer until I tried it myself.