IMHO add the $400 and get the SI version, then you will have 2D, DI, and SI.
All my units are Side Imaging units and I do not use the DI view for fishing. Mostly for demo screen shots. I prefer the coverage that SI has.
With the ONIX, I just turn that function off.
Humminbird Helix 12 SI, 1198c SI, 1198c SI, ONIX 10 SI NT, 360, RC-1