On a flight back in August, the gate agents were making people use the sizer and if you couldn't drop the bag in without having to do any squishing, they were making you gate check the bags. My bag caught on one of the sides and when I reached down to shift it so it didn't catch I got told to stop. They did allow me to lift it back up and drop it down showing that it did actually fit, but the guy in front of me was forced to check his duffle that could've fit with squishing - because they said it had to go into the sizer without force.