i used to play hockey right through school and i was pretty good at it too(yes slag me all you want), if a gum-shield can protect your teeth against a hockey ball then it should easily be able to protect you while on the water!! You can still shout and talk(muffled) while wearing one.
I wouldn't bother going for the full face protection, its far too excessive, considering you will probably not be running any high drops!!
All mouth guards are the same and do the same job, just make sure you tightly mould it to your teeth.
my $0.02,
rich