Just converted my Helix 7 to hardwater but experimented this summer on open water.
Biggest pain in the ass I had/see is that when you switch from one mode to the other it "forgets" all you settings.
Yep Humminbird knows about it.
Spend all summer getting it "tuned" in then switch modes and it's all gone, damn!
One huge feature with the newer models is the ability to contour map (Bathymetric Maps)! Have to drill a few holes or map it in the summer from your boat.