[RarlyL8]

I see M&K has a similar unit but it uses 2 sets of exhaust pipes which just look silly IMO

Our systems are build to order, specific for the engine, application, and what the owner wants. Many of the GT3 backbox systems we have built are fully functional, using all 4 inlets of the muffler with active exhaust valves. Some of the systems block the upper inlets and just use the bottom, some block the bottom and use the top, some use all 4 with no valves, it's your choice.
It is important to note that one system does not fit all applications. The muffler sits in a much different area in an early 911 chassis than it does in a g-body with impact bumper. Large engine transplants also require custom fitment. We've done everything from stock 2.7L to full race 4.0L engines. Flow is key so some configurations won't work for big heavily modified engines.