I installed the Hale door myself.... dead simple. I had a smaller cat door which was in the wall when we bought the house, and I removed it to find it was well installed with studs framing it, but a few cuts with a reciprocating saw removed them, and the Hale door installation instructions were very very detailed, and the installation went smoothly. Our 3 Westies took to it immediately and love it.
I highly recommend this door.