Is all DEF the same?

I had been buying BLUE DEF for the past year. "Gold star, premium, blah blah blah..." Recently at the auto parts store the clerk showed me they had FRAM Def. It was literally half the price. So I bout 2 jugs, put them in and have been running it now for over a month. Today at the same auto parts store someone was buying BLUE and I tipped him to my recent find. To my surprise, another clerk said not to buy the FRAM brand that it can cause issues? I was like, wha..? Then why are you selling it? In all my research everything says that DEF is DEF is DEF provided it has the right percentage of urea to water. I mean, it's just atomized into your exhaust to neutralize harmful emissions. So is fancy DEF any better than house brand stuff? What about DEF at the pump - who knows what brand that is.