OK, I am one of those that does a lot of fishing in areas of 6 feet or less. (Flats of Florida coast.) To me and IMHO the idea that side imaging is of little use it these depths is just plain wrong.
It may not show you the same king of picture that you see in deeper water, but in these depths, a 6 inch depth change can mean so much, the side imaging will show you not only where the change is but in what direction the runoff goes and in a picture that is unmistakable. When you are fishing shallow water, this information can be, well, invaluable!
I only have a 797C2, but I am absolutely drooling over a 898C, BUT, don't underestimate just how much info I get from that little 797C2.