When I had my breast reduction, my plastic surgeon recommended using Mederma to reduce my scars. I bought a Walgreen's version of it that worked quite well. I didn't need to use it on my lap-band scars because they disappeared so quickly on their own. Later I used it to reduce the appearance of a scar from a mole removal.
Recently one of my puppies scratched the top of my hand badly. Even after it healed, it was fierce-looking. I don't mind scars where my clothing hides them, but this one is very noticeable. I had used up my original tube of scar gel, so on Saturday I went to get another one. I couldn't find a "generic" version, so I bought the real Mederma (it ain't cheap). I applied it to the scar on my hand on Saturday night and forgot about it until Sunday morning. Literally overnight, that scar had been transformed from this angry red, raised, gaping gash to a faint pink, flattened mark. I was amazed.
So I would have to say that in the case of Mederma, it really is worth paying extra for the real thing.