Not sure about Storm scopes on boats.
On airplanes yes, because you are fast enough to fly away from a thunderstorm if you see one on the scope while IFR.
On a boat you will see it visually in day-time and see the lightening at night and can try to run.
If you get caught in a squall on the water, the storm scope may not help anyway..(Too late)
Perhaps the more experienced Captains on this here board have a different opinion on the Storm Scope..?