The echo 551dv is a new fishfinder from Garmin that offers both traditional broadband sonar and down imaging. It produces probably the clearest image among fish finders in its price range. Garmin echo 551dv also stands out from the crowd by giving the user the ability to view the output horizontally or vertically.
GPSMAP 840xs is a part of the new series of fishfinders from Garmin that support down imaging as well as side imaging (Garmin branded those technologies as DownVü and SideVü). Down imaging is built-in while side imaging requires a GCV 10 module that is sold separately.