Can someone give me some guidance on Garmin map subscriptions? I picked dup a 93sv and am slightly disappointed to see that I can't change the lake level without a subscription. Looks like I need Vision+, but want to verify I am not missing anything. Is the mapping that comes with the subscription that much better than the preloaded map? If I purchase Vision+ once, I lose the ability to update after a year, but retain all the mapping and features (including lake level adjustment), correct? Thanks!