I wasn't quite sure how to put in this mouth opener, but my husband had no problems putting it in without instructions. Once I figured it out though, it fit perfectly, was comfortable, and didn't hurt my gums or teeth.

Our mouths are different sizes, and neither of us had issues with the sizing.

I can still talk a bit with the guard in, but it is definitely limited - I've been using them for my weekly teeth whitening, and it helps make the process simple and allows for my whitening agent to cure properly.

Overall, they feel comfortable, are durable, and are easy to clean after use.