It worked, but make sure you measure carefully
I’m writing this even though I don’t think you’re as silly as I am... I tried out the cat flap in my old house before moving and everything was fine. In the new place, as soon as I installed it on the glass door, I realised it stuck out too much and stopped the shutter from coming down. Even though it was clearly written not to drill or cut the cat flap, I did it anyway, and of course I ended up cutting the circuits and now it doesn’t work anymore (it doesn’t recognise the microchip).