Again, and not to go in circles, and I'm not trying to argumentative here, but, with all do respect, you may not be familiar with all the technology here with the Birds ….
Using my Humminbord Onix Unit, which is 10 years old,
I can view my SI transducer, AND my 2d high def, both resident to the Onix, AND My switch-fire transducer, from my 999, AND my minnkota US2 transducers on the same screen, real time, live.
4 sources, 4 different transducers, originating from 3 different units and transducers. I am sure I could add a 4th source, like my bow mount unit as well (if I added yet another transducer somewhere).
I was able to do that in 2013 when I installed these units on day one. That's nothing special.
Don't take my work for it ..... see it for yourself ...…
Networked, the Humminbird owner can control, view, operate, deploy and retract, the minnkota trolling motor, a shallow water anchor like the talon, a cannon downrigger, use I-pilot controller for gas kicker, or any of the sonar units, any transducer, from ANY networked head unit ………. LIVE
Things like live mapping, pre set tracks, waypoints etc.., obviously, are included in that same bundle of compatible products.
see it for yourself ….
https://www.humminbird.com/learn/one-boat-network
Like I have always said, both are good brands with a solid reputation of innovation and quality products. What you choose should depend on what each person wants or needs and what their budget may me. But there is no way anyone can say one unit is better than the next in all areas - as both companies leap frog each other with cool new innovations we all benefit from. (and spend more money on I guess)-lol.