I have never heard of Rev9, but can tell you that with any kind of muffler delete, you are going to have a lot of drone... specially in the low RPM range. This can be very hard to live with over time. Most mufflers, even the aftermarket ones have some sort of built-in chamber that cut down particular frequencies responsible for droning.
I personally bought a used 335i M Performance Exhaust (MPE) from this forum ($600), along with deleting both resonators from the midpipe ($100). All in all for ~$800 including labor... you get a refined BUT pronounced sound. Try looking for an exhaust that re-uses the factory flap connector found on the driver side tailpipe. Not having a flap or having it open all the time also introduces noticeable amount of drone.
If you are handy with tools and have access to a welding shop, this stock exhaust modification could be one of the cheapest options to consider as well:
https://f30.bimmerpost.com/forums/sh...d.php?t=819125