Ideal Pet Soft Cat Flap Door

Ideal Pet Products
Pros: easy to install, inexpensive, soft flap won't pinch cat's tail
Cons: separate insert to *lock* door
Bought this to install in a hollow-core door between kitchen and basement stairs.  The main reason for buying this one was the soft flap which would not pinch a cat's tail it they were too slow going through it.   

It was easy to install, even for 2 novices who had never used a jig-saw before.  The telescoping frame hides any jagged cutting edges, as well as the hollow space in the door.

Ruby wasn't sure how to use it at first, but got the hang of it quickly once we enticed her by throwing treats through the flap. 
   It makes a small noise when she goes through it, but nothing loud enough to wake you at night.

It does not have a locking mechanism, but does come with a hard plastic insert, which can be used when necessary to "lock" the door.   That would be the only *con* as the insert has to be stored separately from the door, but as we rarely use it, it is not really a problem.
Purchase Date
Pros: Durable, inexpensive
We have four of these doors, three of which are heavily used by multiple cats. The oldest door was put in in 2008, the newest about a year later and they are still doing fine. The plastic flap is clear, thick and sturdy, but light enough that none of the cats have any trouble going through it. The entire unit is very easy to clean (I use a mild solution of dish detergent). The only negative comment I have is that, over time, the flap curls in a little on the sides but the flap is replaceable if that gets to be a problem. These units are intended to go through doors but we have all of ours framed into regular stud walls. I have no doubts that the flaps would also work very well if they were installed as intended. I took off 1/2 star because I'd like the frame to be just a little bit wider.