You will appreciate this cover the first time you slip and fall when hiking in dusty terrain. Use lots of rubbing alcohol to lube the valve and the cover to facilitate installation. It is actually easier to install the mouthpiece through the small end of the cover. I have tried it both ways.
Pros: Works as it should
Cons: Difficult to install
This review was written in the old system and had content requirements that are different than reviews written today.