I looked at both of those units, went with the mark 5 pro. The guy at bps said "friends don't let friends buy garmin" LOL. I read all the reviews (mixed at best), but from what I could gather, Garmin is just entering the low end/entry level FF market, and I was a bit skeptical of the new units. I went with the Mark 5 pro and like it so far as I have had Lowrance for several years myself. It is a bit difficult to get adjusedt to your liking because of the menu, but its not that bad. Plan on spending 2-3 hrs getting it set like you want it if you go with the mark 5.
GO BIG ORANGE !
I meant to behave, but there were just way too many other options available at the time.