I haven't read any reviews on this particular product, I know some products that are added to the water the manufacture only claims to "relieve" bad breath, and has things like mint added. I wouldn't use something like that, but if there is some type of documentation that it removes tartar, I might be interested. The problem I have with adding to water products, is that you have to add it to the water at all times, and the dog may ingest more than he really needs if it's a hot day. Other products you put on the teeth, and leave for a period of one half hour, and it seems like they would have a better opportunity to soften tartar. I would beware of any product that claims tooth brushing is no longer necessary. Teeth are one of Yorkie's weaknesses, and as a breed are especially prone to tartar. We use Petzlife to soften tartar, as well as tooth brushing with a dog toothpaste. I also use hard Bully Stix to help clean teeth. There have been some good reviews of Petzlife tooth gel for removing tartar, we've only used it as a preventative, so I can't comment on it's effectiveness, but other people have recommended it. To remove tartar, you have to use it daily over a period of a month or so. Here are some before and after pics.
PetzLife Products Inc - Products For a Healthier Pet