Muffler question- flowmaster vs. ?

An X-pipe makes the engine sound more 'mono', instead of Stereo with two seperate tubes.
Also, the mono-sound makes the car sound more like a modern car.

There was hardly any power gain to be measured, and if any, it would be just a tad at the higher rpms, accordingly to David Freiburger and Steve Dulcich in one of their YouTube-episodes.