I wouldn't hesitate to buy a used Lowrance unit, as long as it's not a really outdated model. Guys will pull them out to replace, or to sell, and they're still in good shape. Factory backing is outstanding on their products. Do your research on the latest and older models to determine if updated chartpacks are available. If you can find one cheap enough then even if it went out and you had to pay to fix it you shouldn't have too much in it. I got my GPS antenna on ebay for half of the cheapest price I could find for a new one, worked perfectly. Mounted it on foam tape under the windshield. Same for the chart-chip, online for half. Lowrance is not quite as good as Garmin for GPS mapping.
The other issue is the head unit is just the display. You still need a GPS antenna and 'ducer, and a chart chip. But may find one with everything to go with it.
A 5" screen is big enough to display one or the other, but not both. I think that's what Grog was getting at. I have one but only run one or the other at any given time, and back it up with a hand-help Garmin GPSmap-60CS. I'll use the nav-to rose on the handheld and put the chart up on the Lowrance. I'll use the finder when I'm close to shore or for fishing, and it has a temp sender in the transom-mount 'ducer. Very rarely split the screen.
For a smaller boat I think it works out good, and that size will fit in the box or you can flush mount it in place along with your radio.
