When I bought my center console it had 2 crappy 5"s at both places. I replaced the console with a Helix 998 C SI, and finally my front 5" died. I can get an 898 C SI for the front for about $400 or could get a new network capable Helix 7 DI for $600. As I haven't had SI at the front, do people really use the SI capabilities at the front? Or does turning the trolling motor kind of make this hard. Other thing I like about my 998 is it has 3 presets. Wondering how much better the newer models DI is over 6 year old technology in the 898.
The DI models have true Down Imaging from a Down Imaging crystal in the transducer. Your 998 and a 898 do not have Down Imaging. They have Down Imaging views
created by blending the two SI pulses. The DI unit's image will be sharper.
The Helix 5 and Helix 7 models do not have the three favorite view buttons. Takes at least the Helix 9 for that feature.
I use Side Imaging at the bow with SI transducer on the trolling motor and don't use Down Imaging at all for fishing, just demo screen shots.
SI shows the same thing as DI, just more of it since it looks to the side and also displays the water column.