As far as I'm concerned there are only three things you should put in an A/C system- pure R-12 or R-134a, the proper oil and a UV dye to help find leaks. I would never use a sealer of any type, fix the leak.
You can preach it all day long, but some folks will not have any of it. I sell the stuff every single day at work. We have pamphlets on it that come out all the time to help warn customers about what works, what doesn't and what to stay away from.
IMHO, I don't think the auto parts stores should even sell refrigerants. People are "gonna do what they're gonna do" regardless of what they are told is right or wrong.
We get people on a very regular basis wanting "just the fittings" so that they can charge R134a right on top of R12. When you try to tell them not to do it, you get that deer in the headlight look.