I have (also) observed quite high "constant" CPU demand of this extension, what leads to proposal of seemingly simple workaround, what would fit my personal workflow preferences better at the same time:
Have extension set to do "nothing" for most of the time, and invoke it just on demand.
If you are seeing constant CPU load, then something else is going on that needs to be fixed. But, I think it is worth it to have a command that lets you run the spell checker when you want.
I have (also) observed quite high "constant" CPU demand of this extension, what leads to proposal of seemingly simple workaround, what would fit my personal workflow preferences better at the same time:
Have extension set to do "nothing" for most of the time, and invoke it just on demand.