Some people are against it because it does contain the antibiotic Tylan and they don't think this should be used for cosmetic reasons. However, sometimes the tearing comes from a low grade infection, and the antibiotic can clear it up. I wouldn't use it long term though, and the people who say it works, say the results are fairly immediate. Joey had really bad tearing after a food switch, you want to make sure something in the food isn't causing the tearing. Here's some more information on tearing causes and cures.
Factors to eliminate Tear Staining - by Tonia Holibaugh - Rhapsody Maltese