I have three that I use.
My favorite is a nuvi 3490 that is my second. It has a glass screen so it is easy to see and use. It is perfect at any time except when it is raining.
I bought a Zumo 660 for the 2016 Cannonball and used it alongside the 3490. It is clumsy and ugly, but works in the rain. It has a hard mount on the Xmax.
I received a Zumo XT for Christmas this year and have been using it since. It is not as easy to use as the 3490 but close. I have had a few issues with it going dark or cutting out on rides, so I still don't have full confidence in it yet.
I have RAM mounts on every scooter and power on all but the Zuma.
Routes are programmed into each using My Route App mostly.
If set well, routes are easy to follow. I rarely make a wrong turn and when I do it is usually my fault as I turn off the sound and don't use any bluetooth to the helmet.
Simply follow the purple line.
Bill