Orac has just been persuaded to come in through it, it correctly unlocked for her, and she didn't get stuck in it, so it's looking good for now...
I do note that, while Staywell make flaps for larger cats/small dogs as well as their standard sized cat flap, Sureflap only seem to do one size, so they'd work less well for those of you whose cats are larger than ours. I guess this is probably a limitation of how far away the cat's chip can be from the reader when it's deciding whether to unlock; if you had a larger flap and a small cat then the chip might not be close enough.