A solenoid or relay does not (usually) include a diode. Nor does an isolator have to have diodes.
...diode isolators. IMO the worst of the lot - the alternator has to up its output by the diode drop to maintain proper charge voltage - and which battery does it pick for that? Does it overcharge one or undercharge the other....?
And then the huge heatsinking - the diode (voltage) drop x current - say 0.7V x 10A = 70W.
And you cannot parallel the batteries....
Diode isolation is for signaling and small power - not big!