The cryo cuff, and similar, only ice the front of your knee, unfortunately. I wish the companies that make these would change them to completely cover the entire knee, but until they do, use it on your knee and add ice packs (don't forget to add a cloth behind both the ice pack and the ice machine cuff to prevent frost bite) to the back. I also recommend an electric one if possible as, IMHO, constantly raising and lowering a bucket of ice and water at any time would be a pain, and especially so when you're recovering from a TKR!
I don't know much about the Cryo Cuff brand, but have looked into other brands and I'd avoid the DonJoy; it's a great one when it works, but IME it breaks down constantly and needs repair and replacing often. I've heard the Breg brand machines are good and reliable though. Also, since you're in the USA, check with your OS, your hospital and your insurance to see if they provide one; mine does so I didn't have to buy one, but definitely would have if they hadn't provided one.