You mention the Montana 680, that is the same GPS as the Montana 610 only with an internal camera. If you carry a cell phone or other camera then you probably don’t have a need for a GPS with a built in camera. Unless walking with the GPS in hand it’s a pain to remove the GPS from the mount just to take a picture.
As a rule the Montana 610 is cheaper than the 680.
The Montana 610/680 is a good on-road/off-road GPS but can be a bit complex to set up to use a lot of the special features. The Montana 610/680’s strong suit is off-road use as it has many built in features along those lines.
The Montana 610/680 can also be rotated like a cell phone to use in portrait mode or landscape mode. This can be a plus in some situations depending on if you ride in North-Up routing (north always up) or Route-Up (direction of travel always up).
As for mapping on the 610/680, you don’t necessarily need the Garmin North American mapping as there are some free or very cheap alternatives that will work great on the 610/680. One of the nice features of the Montana 610/680 is the ability to load a number of maps then pick and choose the one that you want to use.
The one down side to the Montana 610/680 is that Garmin has added a feature that requires authentic Garmin mapping so it won’t work with locked pirated Garmin mapping. It still works fine with 3rd party mapping and Open Street type mapping.