Are all Galvanic Isolators the same? Are the GUEST Galvanic Isolators from
West Marine as good as any others? I need to install a 30 AMP Galvanic
Isolator.

Should be pretty close....the main component of a galvanic isolator is a bit of
solid state electronics that allows current to flow one way, but not another.
(I think it's a diode, but 296 people will correct me if I'm wrong.) Odds are
that nobody builds their own diode, probably bought from a common supplier.