Lowrance HDS5-M 2nd Gen here. Having a hard time coming from 15 years of Garmin, like the layout and features. I got the Lowrance Sonic Hub stereo that goes with it for an integrated easy install package. If you have a metal roof and mount it in the dash, you will need an external antenna.
I do notice that the topo maps have a heavy preference to water instead of land and I find that irritating in the desert. Might be able to filter it out, but I really have not spent that much time playing with it yet. I still have my trusty Garmin 276C mounted to the cage in case I can't get what I need from the Lowance