I have one! It is awesome!! I'm a geologist and when I would do field work, my knee would swell up to the size of a soccer ball and never really go down again until I'd been not doing field work for a week or more. With my new knee, there are days when the only thing that doesn't hurt is the new knee. Get...it...done!
Having said that, be ready for (a) lots of pain and (b) doing all the rehab with a will. Yes, it hurts. Yes, it hurts worse during rehab. YES, IT'S TOTALLY WORTH IT!!
2 bits of (unasked-for) advice: (1) Don't get both knees done at once. I know that means duplicating the pain, but I don't see how you can rehab two knees at once. (2) Get your ortho to prescribe a machine that will flex your leg for you for the first couple of weeks. The biggest hazard with knee replacement, as I understand it, is when people won't do the rehab (i.e., won't flex their legs) because it hurts too much, and what happens is they end up with ever-decreasing range of motion. You do NOT want that to happen because you won't get it back (apparently people think they can restore the range of motion any time--they can't). The machine keeps your leg flexible (and increases the flexibility) while you're getting past the worst of the pain. While it hurts when the leg flexes, it hurts most when you have to do the work of flexing it. So getting past that first two weeks with less pain than it takes when you do the work yourself is really good.