Not sure about the application for a guitar however the hand planers are nice for some jobs.
I have the Milwaukee cordless 18 volt, I got it to adjust doors on an older home that were not standard, worked like a dream. So would have a normal hand plane, I more or less just wanted a new toy for the job.
while it has a great deal of adjustment at 32'nds of an inch, I would really struggle to work on material as thin as a guitar panel.
To make that clear, it is a lot easier to make an error with than a hand plane and that error will be several times worse with it than a hand plane.
Nothing wrong with either you have shown, would buy either but done think I would buy any for the application you are talking about.