Hi mate,
I would not recommend getting any of the mould-in-the-mouth brands. I am a dental professional, and i make mouthguards, and it's much better to have a custom made guard, because then you can choose your thickness and make it totally to how your mouth is. Go to a dentist and ask them how much it will cost. All that happens is you have an impression taken of your mouth. You can choose colour/design etc. I actually make them for a living, pity i can't do many more than i get because i could make some awesome designs like flags or with your name in it etc.