Whichever you get, absolutely go for it if you've already got the shifter. I've got the single piece Barton so I can't say much about the two post, but once you take off the stock bracket and compare it to the aftermarket, you realize how much of a joke it is.
Mine did increase the noise of the transmission in the cabin slightly, but I dig it. I didn't buy a mustang to not hear the car in action, so the more noise the merrier for me. That being said, my stock shifter just sounds and feels more solid locking in gear.
Whichever one you go with I'm sure you will be pleased!
2014 Oxford White FP6 - K&N CAI, BAMA Tune, SR Strut Tower Brace, JLT Oil Separator, Barton Shifter Bracket, C&L Billet Aluminum Shift Knob, Interior LED Lighting