I was confused on what Navionics product to buy and the Navionics Moderator at BBC had this answer for me. Question was what is the difference between Navionics + and Hotmaps premium. Same price for Navionics + US and Canada and Hotmaps premium southeast or other region. Copy and pasted.
The Hotmaps Platinum has Satellite Overlay, 3D function, Port Photos and Community Edits. All that additional stuff takes up memory space.
Both the Hotmap Platinum and Navionics+ products have Nautical Charts (Navionics maps) and Sonar Charts ( user sonar log generated maps).
Bottom line is the map details are identical if updated the same .