@Whoodoo - The description says the universal flaps are also thinner.
I have yet to get flaps for my would-be rally car, but when I do, I know a number of people who suggest going to a truck stop and buying one or two replacement semi flaps. They're thick, durable, and can be cut down to desired shapes. If you measure the general dimensions of your desired flap size, you can determine if you would want to buy one or two semi flaps. They're supposed to run $20 or so.