This extender makes a neat job of lining a tunnel through a hole cut in a wall for those who don't want to have a flap mounted in a door. Looks good, easy to fix, cat seems happy with it. What's not to like?
The price.
For a normal outside wall you'll need five of these. So lining the tunnel will cost you nearly £35 at Amazon's price (£76 at RRP!!). The box it comes in must cost as much as the plastic extender. Why so expensive? Why not offer (say)a 200mm extension as well as this 50mm version?
Try to improvise a DIY solution!