Almost impossible to put the hopper together as the plastic parts are warped enough to not fit together. We had to soften it with a hair dryer and push and shove and bend it with marginal results. Our dogs like the tennis balls for fetch but the hopper is tipsy at best.
I would like to mention that conventional tennis balls are made with glues that are toxic to your dog, and the material that gives them their outer texture is abrasive enough to cause long term damage to their teeth.
Please look into dog-specific tennis balls if you want to use them with your dog.
The box is impossible to put together, rendering it useless as a hopper. The pegs are not aligned properly and are too big to fit through the holes. The worst part is I cannot return it because it came from wit and I didn’t open the box in time.