I would copy that letter and email
it to Garmin marine
. Explain that you have already uploaded it on an international cruiser's blog and ask them if it true. If it is really their intention to render the second hand value of every piece of their gear
worthless. If they really mean for you to use their plotter for three years then throw it overboard
I too have used Garmin's aviation stuff. And I found the user interface unnecessarily complicated and their update service
ridiculously expensive. I went with Lowrance Airmap instead and loved it.
I would never put their stuff on my boat. I would be temped to suggest the law firm commit an unnatural act with themselves.