Hi,
I have a 451s on the rib and use it as backup - I also have a GPS plotter which uses Navionics Gold Charts and to be honest, the information you need for navigation (depth, buoy marks, etc.) are all the same - The Navionics has 3d functions etc. which is just "interesting" than practical!
I found 451s a very capable device and easy to use! the base map is as good as any chart - my advice would be just don't waste your money!
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