If you go with a DSI version, the lake bottom contours and any structure (trees, stumps, etc) will be similar to looking at a picture or the TV, the screen image will continue to update. You will not see any fish symbols or arches in DSI, only white dots. The HB dsi units have both dsi and 2d while the Lowrance units are only dsi or 2d, not both. A 2d unit will have the option of showing arches or fish symbols but you will not see the detail as you will with a DSI version.
Should go to a store that sells 'em, and push some buttons, and look at the screens to see which one you can interpret easily.
GO BIG ORANGE !
I meant to behave, but there were just way too many other options available at the time.