Technically, a solenoid wired as a split-charge relay IS an isolator. It's a solenoid-type isolator, as opposed to a diode-type isolator. They both isolate and are both called isolators.
And yes, I did answer the OP's question. He wasn't asking about the difference between a starter solenoid and a diode-type isolator. He was asking about the difference between a starter solenoid and a solenoid-type isolator. The difference, as I said, is continuous duty rating.
A typical dumb solenoid wired to be energized when the key is turned to ignition is as simple and bulletproof - and fool proof - as it gets. There is nothing to remember.
Sure, some companies do add a switch to give some options, but it's not like you have to remember to flip the switch every time you drive. I suspect most people just leave it switched to automatic and leave it there.
And a solenoid doesn't have the voltage drop issue that diodes have.
I run a dumb solenoid wired to come on with the ignition (not a fancy IBS system - which is just a dumb solenoid with a little brain to decide when to energize the solenoid). Done deal.
Current: 76 E-250, bubble-top, self-contained|couple of old Yamaha enduros
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