I have the Wike trailer linked to above. The trailer is plenty comfortable for the dog, and she would lie in it when it was still. However, once we started moving the dog wouldn't stay in the trailer. She got her front legs out and ran with the front legs while her hind legs were stuck in the trailer. It looked funny, but also unsustainable.

I think a lot depends on your dog and your relationship with the dog -- probably a lot more than the specifics of the trailer.