Get the long poo pipe, it made my HT run really torquey and sound nice and smooth like a Zuma scooter. It's got an expansion chamber and baffle inside. You have to bend it slightly to fit an OCC but it's simple with blocks of hardwood and a vice.
The only complaints that I have are that the gasket for the pipe fitting is junk, replace it with an aluminum crush washer, and the flange for the fitting nut is welded and broke off, it would be worth welding the thing all around and then re-grinding a flat flange that won't break off.
I'll be reusing mine on my OCC with Morini clone, cut halfway to mate to a KTM expansion chamber. Instead of having baffles inside, I'll be putting the cat converter from my broken black cat pipe inside and holding the ends together with all-thread and sealed with copper silicone. It sucks to arrive and smell like a lawnmower, the cat really helps, and I want to keep the bike quiet to avoid BS.