I'm the outlier
Read many reviews, all glowing and not one with my problem.  While putting it on the top gasket (the one with the hole) consistently popped out of the blue ring.  Rats, I was so looking forward to a first shower in nearly a week.  (I'm sure my wife was too.  Solution?  Easy, I made sure boot gasket was properly seated on the lower ring an put a band of surgical cloth tape over the boot gasket.  The carefully placed the top gasket centering it and press the top ring down all around. Now the gasket will not slip out and you're ready for your shower.
Rating: 3 stars