Warning: I am about to post something that most people will shake their heads at, and likely not be happy about.
For what its worth, I have been burned 3 years without a cat in my stove. The first year I didn't even know what a cat was. The first year I burned, I was cleaning my stove, and the cat was crumbling apart when I took it out, so I just threw it away, not knowing what it was. Crazy right?
Well, I have burned three years now without it, because the housing that it goes into is warped, and will not hold the cat. I could buy a new housing, maybe, but its an old stove and would probably have to have Appalachian fabricate it. Then I would have to buy the catalyst.
My reasons for not doing so? I get six hour burn times in my small stove, it heats my house fine, actually overheats the house until it gets to 20 F or below, then it just keeps it at 70. I go through about 4-5 cords a year, heating my house about 90-95% with wood only. I have a rod and brush and sweep my chimney once a month, because it does create some creosote, but its a 10 minute process for me to clean it, I have an easy roof to get up on.
So what I am saying, is my stove does not burn out of control, burns reasonably long, and heats my house very well without the cat. Would I get longer burn times and burn more cleanly with one? Yes, of course. But the difference to me is not worth the money, to be quite honest. I would buy a new stove, but I probably won't be at this house for long.
I am not arguing for everyone to go throw away their cats, obviously, but I don't think its quite the end of the world scenario some people think it is either. Keep in mind, my stove is old, circa 198X-ish, so the CAT design probably isn't as great as they are now. Basically I leave the housing in the back, and close the damper all the way to the housing. This leaves about a 1 1/2" by 6" gap for the smoke to go through in the back. I get a bit of smoke out of the chimney, but actually not very much once I have the stove up to temperature.
So thats my experience. I am sure a lot of people won't like it, but I just thought I would throw it out there, for what its worth.