I have a Humminbird 987c SI seven inch screen flush mounted in console main unit and a Humminbird 5 inch brand new Helix 5 GPS SI top of console gimbal mounted. Both run Navionics charts. They are not networked and do not see my engine which has it's own electronics instrument display.
But, that said, someday, when the ten year old 987c SI dies, if it ever does, I will move the Helix 5 to my kayak or project 15 foot BW and I will install networked (probably Humminbird) units, a nine or ten inch flush in console and whatever five or six inch unit they have at the time up top gimbal mounted.
I like Humminbird, owned four of them, no issues ever, easy to use. Nothing against Garmin, not fond of Lowrance, the others, not sure. No matter what you get you need to be able to run charts. The way I intend to use my current set up is to use my larger 987 for my bottom machine and navigate on the new, faster CPU Helix 5. Or, run the 987 for whatever ever function is currently primary to me, nav or bottom, and use the smaller machine for the secondary function, if you follow.