I can't vouch for Megahydrin's effectiveness on bad breath but I wouldn't be surprised if it is. I'm not sure if free radicals can be a cause for bb, but if it can and it is the cause of your bb I'm sure Megahydrin can help. As it is a powerful antioxidant which neutralizes free radicals.
You might want to try taking parsley caps. I've heard it helps against bb. Hope it helps.