The overall concept is innovative. However, not all adult cats will be ok confined to such a small space. My baby boy Storm felt trapped, trying to find his way out. I, myself, am claustrophobic and he probably felt the same way. I let him out when I realized the backpack feature was not going to work for him. It may be ok if you begin use when they are kittens and can become acclimated. The zippers work fine. It can serve as a regular carrier when expanded. There is an opening to the expansion itself so it makes it easier for the cat or very small dog to walk in from behind. However, I have found it easier to put him in by unzipping the bubble. Using the expansion entrance is tricky because while you're trying to zipper it shut, he's trying to get out! I will be using this as an extra carrier for car trips so he can see out. Also, it helps to have an extra carrier while traveling in case he gets sick and throws up or does the other thing. I am giving it 5 stars because it is well-made, as roomy as his regular carrier, he can stand up and lay down comfortably, room for a small food dish. Just because the backpack feature did not work for my cat, it may work fine for others....it depends on the pet.