Don't get me wrong, I'm not trying to defend this particular exhaust, just pointing out that the concept is not as poor as people think, due to the fact that the l/h box would be the one doing all the work and the r/h one is purely for looks, for example, IF DONE CORRECTLY, there's no reason why a btb exhaust, per say, could not still return the same legendary results but have the addition of a second box, and the reason being that it's got to be far easyer to design a single sided system then add the other side, than to design a proper two sided system, taking into account the complexitys associated with splitting the flow into the two sections has it not?
If we were to look at the duplex systems offered by the likes of remus we would see that the flow of gas into the secondary side is poor to say the least, yet it retains it's status as a "quality" piece of kit.
Pete