The Sherpa bag is very good quality, but the medium size is pretty small.. There's no problem fitting it under a seat.
Our Alice grew out of it at 6 months (female Pug) so we have to carry her with her head/body sticking out.. She's 10 months now and 18lbs, UA still allows her on board...
I was thinking about getting the large size. Does anyone think that we will be denied with the larger size?