I've rarely had a problem with my 22" carry-on on European flights. I've flown KLM a few times. Once, on a very full flight from Milan to Amsterdam, where a sports team was carrying a bunch of equipment with them, they asked us to check our bags. Otherwise, I've carried bags on numerous flights within Europe on various airlines. I have a big camera bag that's my "personal item" that does fit under the seat in front of me, if need be.
The one exception was Iberia a few months ago within Europe: I took two Iberia flights where passengers were hassled to gate check their bags on both flights. On one flight I did have to check the 22" bag. So I put the camera bag that would have gone under my seat up in the overhead bin, using the same amount of space. It saved no space on the plane, but it did inconvenience me and make me mad. (I had some other issues with Iberia - hope never to fly them again if possible.)
And I've taken these bags on numerous overseas flights (Delta and AA) over the last few years without needing to have them checked, even on full flights.