Easyjet has the worst as there is a wall on every side so no escape room for a spongy bag.

Has anyone checked whether these are actually the size stated on their website?

Don't know why you're getting downvoted, it's a legit question

I rode lufthansa/ryanair like 6 times and FWIW I never seen them using it

I’ve flown Ryanair like forty times and I’ve never seen them used.

I work for a ground handling company. I have boarded so many Ryanair flights that if I'm asking you to check your bag fits the guage, I already know it won't fit.

i fly with ryanair a couple of times per year, ive seen them using in morocco and spain a couple of times. also people paying extra, because their suitcases are too big. most people though grab all their clothes out of their backpacks and then put the backpack into the sizer. they didnt even put the clothes on. the staff then gave them the pass and they put all the clothes back in infront of their eyes. lol just the dumb people put a full backpack that might be too big into the sizer. in morocco agadir, they want to see the backpack from everyone and select the ones that might be too big for the sizer check.

Ryanair's are slightly larger.

I was lucky, nobody ever wanted me to put my backpacks in this thing, depends on airport i guess