If you don't need extra cost XM radio or weather or bluetooth go with the Zumo 660 otherwise the Zumo 665 is what you want. I don't need either one so I saved a couple hundred dollars. I also have the H-D fairing mounting bracket because I wanted a clean install, not a bunch of wires hanging around.
Garmin has a new lower cost/feature model, but I'm not up to date on the specs.
Hard to beat any of the ZUMOs.....My Old ZUMO 450 is over 7 years old, sat out in Major Rain Storms, and been used thousands and thousands of miles on Various Motorcycles, Trikes, Scooters, and my Jeep....it's been an "ANVIL".....ThumbUp
Back in 2007, I bought a Zumo 450 and loved it. Unfortunately, it only lasted about two years before it took a dump. Replaced it with a refurbished 450 and it lasted about a year and then died.
Even with those problems, I still like the Zumo series and after going without one for three years, I bought the 660 hoping that it will last longer.