Yes you are correct. Humminbird and Raymarine use several SKUs on the same size screen. for example Helix 10, Helix 10 Down Imaging, Helix 10 Side Imaging. They are all the same unit, but have different software loaded and come with a different transducer. Lowrance and Garmin (for the most part) have 1 unit GPSMAP 7610XSV or HDS12 and then you pic your transducer to go with it based on what you want to see.
The only disadvantage to the Humminbird and Raymarine model is that if you have a SI unit on the back and a DI unit on the front you can interchange them should one go down on you. They will however network all the info when connected with Ethernet. You have a Helix 10 DI up front and a Helix 10 SI at the back. You'll be able to see SI from the back unit on the front DI only unit when networked together
Lowrance, Garmin and Raymarine will all share Navionics+ maps over the network, while Humminbird Helix will not. You'll need two chips with a Helix unit.
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