Tongue scrapers are somewhat effective against bad breath. They can't, by definition, get rid of bad breath permanently, because bad breath is caused by bacteria that live in between the fibers that make up your tongue. Your tongue is more or less like those shag carpets from the 70s-- except mine's not avocado green. The papillae or the fibers that make up your tongue protect the anaerobic bacteria which live in between.
So when one takes a tongue cleaner or tongue scraper, such as these available at therabreath.com, what you should do is apply some of the TheraBreath tooth gel to the edge of the tongue scraper. And then very gently scrape across the tongue's surface so you're getting rid of the debris that rises to the top. But secondly, you're pushing the oxygen compounds of the TheraBreath tooth gel in between the fibers to attack the bacteria. That way you're doing double the work and doing a much better job of keeping the tongue clean and the breath fresh.