I had a Humminbird Helix5 DI installed last year, and guess I would say it's been OK, but maybe a little disappointing -- probably as good as anything else I might have bought. I'm not sophisticated enough with it to make full use of it, but that's the case with everything from cellphones to microwaves, so I'm OK with that. Unfortunately, neither down scanning or side scanning has amounted to anything very interesting so far. The image is good but not as spectacular as I kind of hoped for, and side scan takes some interpretation. (Maybe the lake just turns out to be kind of boring down there.) Down scanning seems to limit out before I hit my usual depth of about 150' or so. But you still have the old fashioned stuff for depth and fish finder functions -- and the GPS tracker is really neat (along with temp and speed). It shows current and past courses, and allows you to duplicate a route without setting waypoints or any of that stuff (another option I haven't used yet). My home lake isn't all that big, if pretty deep -- GPS nice to have, if caught out after dark or in bad weather.
Make sure you have the right computer for downloading software. With H.Bird, it's done on your laptop or other device, and transferred to the unit with a micro card -- so need to know what card is needed, and importantly what system is needed for the download. With H.Bird it's strictly Windows (I run Apple equipment) -- used an old Windows desktop to get the software downloaded. Oh, and find out what's included in terms of lake maps, if any, or what's available.
The sonar is transom mounted on my inboard -- had some concern over that placement, but has worked out OK. I did find that the unit would shut down unpredictably (starting engine, for example, while the unit was running). After some searching on various forums, I found that the solution is to wire directly to the battery (mine goes to the house battery). As a digital unit/display, you apparently don't get interference or noise -- display just shuts down, But the direct wiring has worked OK (wired with an inline fuse).
For all of that, it's fun to have. One of the settings is a virtual 70s style flasher, which I thought was kind of neat. Actually, the thing would probably cook lunch out there, if I knew how to do it. Maybe a virtual lunch.
