We took our cat on his first flight. He wasn't too thrilled, even with his calming kitty treats. However, this carrier was perfect. It fit a little tight under the middle seat on a Southwest flight, had to squish the top and sides a little. However, this wasn't too bad because the rest of the time my cat had a little extra room to stretch. The outside pocket was very practical, and the foldable flaps meant we could make sure he had enough ventilation. The strap is comfortable to carry, we didn't try the shoulder strap because of his comfort. Finally, having the option of dropping him in or through the side flap was great, specially for putting him back inside after security check.