^^ I bought the 300gallon one, and it lasted for about 35 washes. I also apply it pretty liberally too though. They sell resin cartridges, but the resin baggies are all you need and are cheaper to buy.
The one on wheels is pretty convenient. I don't have to permanently switch my driveway faucet to filtered water. I put a two way faucet head on with one connection being the standard hose and a quick disconnect on the other so I can roll out the CR, clip it in, and start rinsing. And when I'm done, unclip it and roll it back into the garage.