Some use a capacitor as well as diodes, others use diodes alone. It is
debatable whether the capacitor is necessary or even desirable. Other than
that, for a given rating, there is no real difference in brand.

The isolator goes in series with the shore power ground and, therefore, is not
needed if there is no shore power connected.

SBC wrote:

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.

Is it true if I disconnect the dock power from the boat when I am not their,
I do not need one?

Thank you