I will start this review by saying I've only used this with pet rats so far, so my review is based on an animal that size. :)
I run a pet rat rescue, and trips to the vet are something we are often doing. I had been using a cat carrier, but was looking for something smaller and easier. Found this wonderful item and haven't looked back!
For SHORT trips (I would not use this carrier for anything more than that), I enjoy the small size. Two baby or teenaged rats fit comfortably, or one larger adult. They can spread out and be fine. We like to fold a blanket or towel on the bottom, since the material is plastic and they would otherwise slide around.
We've even gotten compliments at our vet for these carriers!
One downside... It's not that it's cheaply made, but we have some wear on the carrier. Some of the wire bent a bit (nothing major, still works fine) and some of the plastic pops out too easily (but ONLY if humans try... no animals have been able to yet). However, it's still a wonderful product.
Washing is easy. The cage part actually can be removed and washed, and the plastic part can also easily be removed and wash.
For short trips, this is our carrier of choice.