I dunno, maybe I'm just cheap but I've never felt the need to spend more money on something that comes free in the box with the camera. And quite honestly I don't find the Canon straps to be uncomfortable (I shoot with 2 1D series bodies so I'm carrying a fair amount of weight around.)
As for advertising "STEAL ME": one of my bodies is usually attached to a 500 f/4 and the other to a 70-200 f/2.8, I think those big white lenses and 1D bodies say it much louder than a camera strap.
having never tried an aftermarket strap there's no way of knowing then? the optech strap is much more comforatable than the OEM canon strap and were talking 20 bucks which in this hobby is really nothing .