So does Lowrance. The problem is that it only works if the water doesn't change. If there are waves when you are mapping, tide changes, river or lake level changes, then it's all off. I think if you are looking to map things in great detail in freshwater it could be useful, but for general contours, ledges and that sort of thing it's not that great.
My hope was to find and map pillars that hold cabezon.
If you do want to use it, my suggestion is to leave the rods at home and map everything you want on the same trip when the water is flat, don't do some today and go back next weekend and try to fill it in. Also don't be pulling pots, running downriggers or anything else that might accidentally block the transducer, you want a perfectly clear view of the bottom without any bouncing, rocking, etc.