If you are asking about BW attachment kit for the spoilers, yes they will fit with an Arrow midpipe. I used both of them together. There is a slight contact with one of the brackets that I ground out a small oval and that cleared the contact. Not a big deal.
Big singles like to have large exhaust volume. The cat adds this volume, and Arrow has added a small volume at the same location in an attempt to help. I don’t believe it has much effect, but the Akro exhaust has a pipe that has a huge mid-pipe section, and it seems to help with power production.
The straight-pipe sections seem to reduce power output.
Essentially, it is there to help with exhaust flow on the pulses.
You are correct, it is a pre-muffler and has baffles internally. Performance wise, it’s shown to be the way to go. But expensive and heavier than the other mid-pipe options.
It is very quiet, even more than OEM. I drilled out the “db-killer”, and now it’s perfect. I had an Arrow system that was loud on acceleration, but fine on neutral throttle. It had the bulged mid-pipe.
I am selling both of the those if you are interested.