Product review (5 stars): decent for the price
Not sure what to say about the issues that others are seeing.  Works as described, have opened the cap multiple times without any breakage or feeling like it's about to break.  Great for keeping air and critters out when the dryer isn't in use.  Hasn't discolored or built up lint.

I sort of question the possibility of the cap restricting or stifling air flow and think maybe it should be shaped differently (conical underneath to direct air out instead of hollow which traps the air) but seems to work well and always seats back properly.