It IS garage door seal, though. People say all kinds of things on eBay: electric "superchargers" give you huge horsepower, two-wire resistor "performance chips" do the same, fuel line magnets increase gas mileage, et cetera. It's not like they're charging a ton of extra money for the repackaged garage door seal, but yeah, that's what it is. The point is just to find the stiffness that fits your particular car the best. Looks like stiffer is better with these cars due to the sharper corners, which you can get at Home Depot...
Honestly, if I was going to get something like this "custom made" for universal fitment across all cars I would definitely design it differently. It's just a happy accident that when you take the garage door stuff and turn it on its side it fits most cars pretty well.
-Rog