I think this is actually pretty bad.  One common shape of bottle will easily slip off the smooth metal with a slight bump, and down to floor they can go.  I'll have to do something to keep the bottles from slip sliding away.  If the manufacturer would have coated the bottom of the rings with something non-slip, the problem wouldn't exist.
Small things: The top should fit tighter into its housing.  This is all machine made, so it should be perfect.  There was also a small piece of metal protruding from near the bottom of one of the rings that I had to file with a half-round.