I have traveled quite a bit with my cat, going home for holidays, and I have never had a problem with an airline telling me my carrier was too big or that the cat was too big for the carrier. Sometimes the checking attendant will request that you put the cat in carrier on the counter for them to see, sometimes they don't. Generally I tried to stay within an inch of the max size by the airline - the carriers I've used do smush that much.
I had a Samsonite carrier (don't remember the exact name), and it worked quite well but after a couple years started looking quite beat up and abused. The soft-sided carriers don't seem to have that long of a life span, but mine did see a fair bit of use. I never had a problem with the cat escaping though, which was my main concern.
Also, taking the cat out at security was surprisingly easy the first few times I did it, though it depends on the cat. I would recommend having the cat in a harness and clipping a leash to it as you take them out just in case. That way even if the cat entirely freaks out and gets away, they won't be able to run off.
I would also highly recommend taking away kitty's food 4 or so hours before you leave, and doing everything you can to encourage him to use the restroom before the trip. My worst trip experiences have been when my cat couldn't hold it and went #2 in his carrier. Then the cat's miserable because he can't get away from it, you're miserable because it smells and other passengers start complaining, and there's really nothing you can do about it on an airplane.