The only difference is the 20MHz model can reach 20MHz when used STANDALONE, versus the 5Mhz limit of the 5MHz model.
From a Spooky2 point of view, they are exactly the same, as their limit when run by Spooky2 is 5 MHz for both of them.
If you are not using the generator, better to unplug the power supply, as it uses a small amount of electricity when plugged in, even if the generator is off. This is just to save on electricity, as the generator can be on 24/7 for long periods of time.
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