the mouth piece is ok. It does what it's should. Now there are two things one should note when purchasing!1. The material is very soft, so when you proceed to boiling the mouth piece two minutes in steaming hot water is way to much. Proper way is to: first have a glass of cold water on stand by, then get a small pot of water boiling and then drop the piece in. Very so often remove it quickly to check how soft it is. When it right enough; it will almost feel like semi soft play-doo, gather a mouth full cold water in your mouth, tilt your head back and just slide the mouth piece in (dont worry it wont burn you as long as the water is very cold)2. Make sure you insert the mouth piece properly into your mouth and bite just hard enough so it can form tightly round your teeth. Also tilt ur head back enough so that the cold water does not touch the mouth piece before it forms round your teeth, because once the cold water gets into contact with the piece... it holds it form unless you to the steps all over again