I don't think there is a con. I have had an axillary brake in my Liberty for four years and it helps all braking situations. The only downside is my brake (Roadmaster) it's a pain to install it to tow, hooking up the pedal and cables and adjust the seat.
If you have to drive the car a short distance you have to do it again. Worth it when you have to hit the brakes quickly!!
Congrats justcruzin on your decision,my wife and I did the same thing.
We traded our 2010 FLEETWOOD jamboree sport for a 2007 Monaco knight 38 Pdq, it has a 330 Cummins vs the v10 in the Class C.
I love the low noise and visibility of the DP.