Which cat flap!?

[Saffkat]

Too much choice! We are hoping to keep our foster mum when her kittens go for rehoming so I have been looking into cat flaps.
Are microchip ones really necessary, that is, are other cats likely to come in? And are they reliable, as I'd hate the thought of her being stuck in it out because of a malfunction.
I also read on one review that the manual ones that are visibly locked are less stressful for cats because they know when they're locked or not and wont spend ages trying to open a locked flap.
Also how easy are they to fit? The flap will be going into a upvc panel.
I'd be grateful for your thoughts

Definitely go for a microchip one. You don’t want other cats coming in and potentially terrorising your cat.

We’ve had ours for 3 years and it has worked perfectly. It warns you when the batteries need changing and you still manually lock it if required. If we ever lock them in then I cover the door with something so they know it is out of bounds.

Sureflap. It can still be locked manually if necessary, and yes, you will have all the neighbours cats coming in if you only have a normal cat flap.
Very easy to install and set up.

Another big vote for microchip flap. You don't want other cats coming in and unlike the magnet operated ones you don't need to worry if the cat loses its collar as the chip flap will still work. Had ours for 4 years and no problems at all. As others say you can manually lock if required and you get a long period of warning before batteries run out each time so plenty of time to change them.

Thanks everyone, we do get a few neighbourhood cats in the garden and one who hangs around on the patio eyeing up our cat. She seems quite interested in him too but hopefully not once she's been neutered.
Sounds like microchip is best then.
Definitely don't want a magnet one - not sure I want her to have a collar anyway - do people have collars, I'm thinking the main benefit would be to signal to other people that she has a home and isn't a stray?

We've had to turn off the microchip recognition thing on my parents cat flap as poor cats microchip has migrated further down his back and is too far from the reader (?) when he's trying to get through it - I don't imagine this is a common issue though...
We'd still get microchip ones in the future despite this!

I’ve recently got a sureflap. (I got the smart one because I’m a sucker for information overload.) very happy so far. Cats happy & no intruders. Would recommend getting the larger pet flap over the cat flap.

Both of mine wear collars. To signal that they have homes and they wear tags on the collars saying they are microchipped so in the event of them going missing or being injured people know that they have owner looking for them and that they can be scanned to check for our details.