I have a cat door, thatÂ´s still in the original box
We bought it to put on the window in the bedrom, since that was their "free" room, and the rest of the flat was off limit when we were not at home, not to get males in to mark the whole flat (happened several times before). This is a special door to use in windows.
When my son was born, we decited to put it in the living room instead, and now they have that window, to the living room is off limit while we are out. But we havent got around to put it up yet, since we probably need a new window for it.
What I find important in a cat door is to have the 4 way lock system, and to have a magnetic operated opening, so that the cats have a small magnets fasteden to their collar, so only they can get in. My door has those things, but I also really like the idea of having a brush that would take most of the loose hair while they enter and exit.
Good luck with your project!