pro choice barrel pad under pleasure saddle?

I am currently riding my pony in a pleasure saddle, but I was looking at those charmayne james barrel pads because I heard they really hold your saddle in place, which I need because willow is round and they are also good for there backs. I was wondering if anyone has used one and if it is shaped differently than other saddle pads?

She makes both square skirted and round skirted