Good evening duncanmac,
The Zumo 665LM is a fantastic device and best in class. Yes, it is just as reliable as any other Zumo. Have used it and found no issues. Jump in and enjoy. Here
is our opinion on that device along with a few others.
Also, just had a discussion with another rider on the XM topic. Post #6
may of value to you.
Cheyenne, WY. U.S.A.