Talking as a rugby player here, DO NOT BUY THE CHEAPO SPORTS DIRECT ONES, they're made from such a cheap material your "moulding" barely makes a difference and it will fall out the second you open your gob. Don't have much experience with more expensive boil and bite mouthguards but if you're desperate for a mouthguard (not sure why you would be ) get a fitted one from an orthodontist/dentist so you can actually speak, should be really comfy so you forget about it after 5 mins and it doesn't fall out !