> Only for it to be collected at the gate and put in the hold anyway, meaning we had to wait for it after all. At least they forgot to charge me for the inconvenience, which given the rest of my experience could almost have been considered a mistake from their side.

Having to gate-check can happen with more reputable carriers too, from American Airlines to British Airways. Even if every single bag individually fits, on a full flight, not every bag for everyone can fit at the same time. It happens more often with smaller (and older) planes, which have less cabin space per passenger.