rust coverter

has anyone tried that stuff at wal-mart, yeaa I know, I know.
I was there getting some wax.
anyway there's this stuff that comes in a spray can or a little jar.
it's called rust coverter. it's supposed to covert rust to primer.
anyone tried it? sound like somethin worth tryin?
it's only like $5

Remove as must rust as you can...then use it...but if you don't the stuff is pretty much useless....