When I looked up the 620 I noted someone reviewed it poorly on Amazon for usability reasons, so I just watched a demo/review on YouTube http://www.youtube.com/watch?v=Tm1-1DwYIok&feature=related and the user interface looks pretty good, IMHO.

The one thing that would be a concern in-general though is the use of touch screen control for ANY marine instrument.... On the boat people's fingers are often coated with sunblock or sweat or sea water, and those oils/chemicals are not friendly to electronic screens, sunblock can potentially attack certain plastics and coatings. At the very least they would leave distracting fingerprints (I'm meticulous about avoiding fingerprints on computer screens).

Has anyone else used a touch screen on the boat? Do you find any of these drawbacks?