I think the bloke was not too well informed, yes an end can designed and tested will yield the best gains, but most if not all will give a bit more up top, and not hurt your low down torque.
As said a full system will give a good gain right across the board, with a power comander and dyno work.
I started with a fuel end can, that helped a little, then fitted the arrow link pipes, pc5,and air box mods, this gave me about 10% mid range through to top end, and improved the low end torque too.