Hi.
From the picture, I can tell you right now that you will gain a louder sound. Performance wise, it is not an ideal design. It is obvious that the designers wanted to increase sound, which is why you see what looks like some kind of multiple tube assembly inside that muffler.
A 4-1 header system is ideal for performance at the higher end of the rpm range. That is why you see many racing vehicles using this configuration, while systems marketed towards consumers utilize a 4-2-1 system. This allows for a slight increase in torque at the lower end of the rpm range, enhancing drivability.
Yoshimura products are geared towards the performance end of the spectrum, which is why you do not see their mufflers being designed this way. A good rule of thumb is: shorter = louder. Think of the muffler/header system as a tuning device that sound waves travel upon and bounce off from. The longer the tuning device, the more "collisions" there are, so a change in sound. It's usually perceived as a bit deeper in tone.
Anyways, I have never heard of Dunstall, but I don't think you should compare them to Yoshimura simply looking at the design. They are geared towards different markets.
Also, on a sidenote, many people just change the mufflers on their motorcycles. That does not provide a significant performance increase unless the fuel system is adjusted. It however does change the sound, which is much easier (and cheaper) than changing the fueling and ignition control. A muffler does as its name implies. It muffles the sound by utilizing baffles. This controls of the expansion of gases, which, changes the sound. Similar in operation to a suppressor on a weapon.
But yes. This Dunstall muffler will be extremely loud.
