I use the built in unit on my 2007 Ultra, works well enough for me, one thing you have to remember is that it's more functional as an audible turn by turn system the graphics are basic and really should not be your focus or concern while in motion on a bike (or car for that matter).
The unit is fully integrated with the audio system, and cuts off the music for instructions, the antenna is in the fairing, the unit is weather tolerant, after 4+ years in various weather conditions it's still working great!
2006 VRXSE Destroyer: VRD-941, SG-941
Best time: 9.661
Best Mph: 139.34 mph
Best 60': 1.393