SCUBASailor
Contributor
I was looking at one at the LDS a few days ago. Seems like it was pretty hard right in the package... I as expecting something soft like silicone.
It is notably firmer than a regular silicone mouthpiece, but because it's molded to one's teeth, it's much more comfortable. I recommend it.
Warning: If you do get one, you will see that the directions tell you to bite hard into the mouthpiece when you are molding it. If you bite too hard, though, it will be so thin that you can't breathe through your teeth. Instead, bite until you have indented your teeth in it, but stop when your teeth are still far enough apart that you can easily breathe. I lost my first one due to this mistake.