I got a medium bag for my 22 pound corgi, and it's a perfect fit for her long body. She was weird about it at first, but now it's where she wants to be during thunder storms, too! We got this because we're living in a city which requires that dogs be in bags on public transit. The extra storage space makes this a far better choice than other dog carriers.
The only "complaint" is that one of the buckles was a teeny bit melted/bent. It doesn't effect how the bag works in any way, and I think that it is the reason my bag was in the refurbished section. Again, it's not really a complaint, more of an observation.
I'd suggest this bag to anyone.