I have a 2013 Sport, and I have removed the middle muffler and kept the OEM rear muffler on.
I can personally confirm that while it makes the truck a little louder, there IS a raspy, tinny, rattling sound when accelerating through the 3k-4.5k rpm range. It seems to get louder the harder you press the gas. The "tone" is actually nice, but is overpowered and drowned out by the rattling noise - so that spoils it.
Next, I kept the middle muffler off, and had some Flowmaster Force 2 mufflers (for the Mustang 3.7) welded on, in place of the rear muffler. Without the middle muffler on, it sounds like shit. Very loud, very raggedy, and very rough. It didnot sound like the Mustang, at all.
So, I kept the Flowmasters, but welded the middle muffler back on. Now, the tone is nice (but NOT like it sounds on the Mustang), but it has too much bass. In the cruising rev ranges, it often soudns like I have a subwoofer playing a constant tone at low volume. The radio easily drowns it out, but if you have the radio volume turned down, you will constanly hear it.
I will probably buy some different resonators - I'm thinking Magnaflow, to mix with the flowmaster. The 3.7 is capable of some great sounds, you just have to have the right setup. I'll report back when I get the new resonators/mid mufflers welded on.