I used a 660 for couple years before it died in the crash that killed DR 1. Great unit, replaced with the newer, roughly equivalent, 396.Been using a Zumo 660 for a decade or so. Recently gave it a present of the Lifetime Maps upgrade, as this model pre-dated LifetimeMaps being standard. It interfaces with my Sena BT in the helmet for turn by turn reminders, and it can store and play music, though I will usually play tunes from the phone as it has more storage. It will also route phone calls through the Zumo, but I haven't found that feature particularly useful. All that adds is giving Zumo the ability to override phone audio for the turn notifications.
The 660 has been thoroughly tested in all kinds of bad weather and on rough road surfaces and it just keeps ticking along. Really can't ask for more. It was ridiculously pricey at the time of purchase, which is why I put off upgrading the map license for so long when for a little more than the price of the upgrade I could purchase a whole GPS with lifetime maps. Only without the waterproof aspect needed for motorcycle use. Kept waiting for a sale on Lifetime Maps, and now was riding into areas where the roads had changed significantly and decided to bite the bullet.
It is light, rugged, handy, easy to use, and removes and fits easily into my jacket pocket at stops when leaving the bike, or to bring into a restaurant to sit and ponder the route ahead.
It works very well with Garmin's Basecamp software for creating routes, that is, the 660 paints the route exactly how I laid it out. Anyone finding one of these new or used would likely be happy with it.
The wife got a Zumo 590 with a bike, and it redraws every route I upload to it from Basecamp. Very frustrating, as I otherwise do like the display. Maybe I can dig a little deeper for some setting that fixes this, so far, haven't found it.
One annoying thing with most GPS devices I've used is how the map layers disappear those backroads I'm riding just when I get it zoomed out to the perspective I prefer. So, I have to keep it zoomed in one or two ticks closer than would work best for me. This is more a map thing than a GPS thing, but may be something that would bug others. Unfortunately, you really won't know if it is an issue until you have any GPS on the bike and are using it.
Which part, the lack of a reliable GPS or me being in front? I might have to object to one of those two...I guess I'll have to fix that next time we ride together...