I use to have the old school black/white 2d sonar units (from the 1970's to the mid 2000's) but wanted something that showed more detail & in color ... so when I got my latest boat, I bought a Lowrance Elite 5 DSI from a fellow member. In essence, I skipped right over several years of color 2d units, straight to Down Imaging. There's an 88pg sticky thread (started in 2011) on this forum, showing my ignorance and my desire to get the unit set up and working for me. Fast forward to late 2017 and I'm dialed in on using the Down Image technology and then .... bam !! While trying to plug the unit up, I ended up breaking one of the copper wires in the back of the unit. A unit that's long out of production, by the way. So I'm still looking for a broken Elite 5DSI so I can salvage the electrical connection assembly from it & fix my old unit. In the meantime, I've purchased a Hook 7 ... which is basically a Elite 5 DSI with a bigger screen & 2d sonar capability added back in. I haven't mounted it on the boat, yet ... but I have manually added all 200 waypoints that I had in the DSI unit (not from the unit itself, but from the GPS coordinates that I had written down).
The main reason I chose the Hook 7 was because it offered virtually the same setup as my Elite 5DSI, on a bigger screen, on sale at my local Cabela's ... for less than what I paid for the Elite 5DSI. The only minor negative things about the unit are the large transducer and the bracket and the power cord & transducer cord are separate & have separate connection plugs in the back of the unit.