My testing seems to show that povidone-iodine mouthwash (which can be DIY'd; just dilute one part 10% povidone-iodine solution, eg Betadine, with 9 parts water) is far more effective against bad breath (not to mention seemingly being highly effective against the bacteria that form plaque) than the usual alcohol or peroxide-based stuff... and it sticks around for a while, continuing to inhibit bacterial growth for a long time following use.

So now I'm wondering why it isn't more widely used.