I asked this question myself, after researching I decided that it wasn't significantly harmful in any real way, some argue that it's terrible purely because its an antibiotic but since it only attacks very few bacterias it doesn't have the devasting effect other antib's do.
Link v explain about it better than I would be able too.
Tear staining, a Real solution
I've personally used angel's glow, if you're able to and get the correct dosage it is cheaper to just get tylosin because that is basically what these products are with perhaps some fillers and hefty price tag.