To add a bit, I thought Sherpa was sturdy in comparison to other soft sided carriers and the zippers were strong, but it's been a while and I don't know what else is out there these days.

In favor of all soft sided carriers - easier to manipulate if it's not a perfect fit under the seat for whatever reason.

Main problem for me with any softsided carrier - not always that easy to get the zipper closed if you have a cat intent on not being confined!