We're on our second or third cat flap, I forget which. These CatMate doors are sturdy enough until a dunderhead tries to force them outward when the tabs are set to allow "enter only" (or vice versa). One of our cats can open it the wrong way by yanking it anyway... the other one, bless her, is too thick to work it the right way around half the time. A bit of superglue and duck tape held the old one together, more or less, while this replacement door was despatched.
Last time I brought a whole 'nother cat flap and cursed loudly while incompetently installing it. Replacing just the flap, on the other hand, was easy peasy.