I have the 8.4 an in my 2013 2500. I have found it useful. I also have SirusXM traffic and I wasn't happy with the interaction of that system to the nav system so I turned that interaction off. It took too long to clear navigation re-routings after problems were cleared and it would have me get off at an exit, cross over and get back on the highway.
I like it for general navigation and routing.
"You cannot reason someone out of a position they have not been reasoned into"
Al, K5TAN and Missy, N4RGO
2002 Classic 30 Slideout
2013 Dodge 2500 Laramie 4x4 Megacab Cummins
2001 Safari 25 RB Twin (Gone, but not forgotten)
WBCCI 1322, TAC FL-39, AIR 82265