Our pup was instantly in love with using this dog runner and had no apprehension. The design is sleek and based on our test runs using it ourselves (to verify it would support our pups weight when he fully grows) this device is solid.
The one thing I wish it had though is the ability to switch the side door to the other side. Unfortunately the latch system is designed and integrated to only work from one side of the machine and not the other. This wasn't a deal breaker though, but just a nice consideration for future designs.