The 492 is a model before Garmin came out with the 44x and 55x series. IIRC, it has the US coastal charts preloaded and can be used with a sounder as an option. The user manual for it can be downloaded from the Garmin website, here.
Slightly less resolution that the new 5x5 units but still good. Good daylight viewing. I prefer using the "highway' view on this GPS when sailing to a waypoint, which is not available on the new units. No need to upgrade unless you want a bigger screen.