It last a good 5-6 months before refill. This is referring to 20z Paintball co2 tanks. I have a two 20gallon long tanks, and a 30gallon tank. All 3 have their own Paintball Co2 tank, along with it's own On and Off valve and each individual co2 diffuser. With expection of my 30gallon being run on a 24oz Paintball co2 tank.
So 3 in total. They last pretty long doesn't take up space and is fairly easy to rig up. Teflon tape is a must or else it will leak. Test the on and off valve once you have it all hooked up and tighten with a bucket of water before final use.