The bad reviews on this seem unjust. I have used this guard and never had any problems. It is held in my mouth by the fact my teeth grind. There are 4 types of guard available so make sure to check which one would suit you
I have not been able to use it, it's uncomfortable, makes me salivating way too much and I cannot close my mouth while wearing it.
In other words I cannot sleep with dental guard.
Said that, the delivery was fast.