This is the greatest carrier.  My 7.5 dog traveled in it cross country on 4 airline flights and the flight attendants and other pet owners were impressed with how easily I managed compared to other carriers.  It rolls easily and my dog loved standing up with the top zipper open so she could see where we were going.  When it rolls flat to go under the seat it was difficult for her to stand so she stayed lying down.   I love that there are zippered "windows".  It secures into a car with the seatbelt and there is a tether inside to hold the dog from falling out.