I used these carriers to fly my and my two cats to California for the holidays.  I was really worried about them fitting under the seats but they fit perfect!  One of my cats had a real problem with flying and tried for 3 hours to get out of this carrier.  It was terrible and I was worried about him tearing out of the mesh but he only tore a small hole in it.  I was so amazed at how well it held up.  Needless to say I wont be using these for flying but they did their job! One of the cats was 15lbs and one is 10 and had no problems fitting in it.

One bad thing is that the wheels dug into my back but I wasnt going too far so it was ok. I also wish there was more padding in it but we solved that with putting fleece in there.