Ive had mine 3 years and 3 weeks. Paid £58 for it then. Changed batteries twice. Works great. Cat uses it all day long. The only way other cats get in is by tailgating. It happens when the nearby stray cat is really hungry. The sometimes isn't a problem. Before other cats were in and out as they please. Was costing a lot more in cat food. It is definitely worth it.
It depends how often you lock your pets out. We lock ours out daily between certain hours. If you never lock them out it won’t ever break.
The big one is currently £65.59 https://www.amazon.co.uk/gp/aw/d/B009NH6NR0
couple of weeks ago paid £63.99 for the larger pet door version from Fetch using a 20% off discount code. took a few days to get our 3 cats used to it, but followed the advice from sureflap i.e leaving it unlocked so no clicking sound for 24 hours, then during the day the next day we taped the flap open with the locking function on so they passed through getting used to the clicking sound, 3rd day had it normal and they were ok. very impressed with this flap and now we don't have neighbour cats in the house, and the one of our cats that started spraying indoors has stopped. well worth the money with happier cats.