Now, Bee, you're walking in my woods. Surely someone as frugal as you wouldn't buy a fancy electric doohickee to do the job of a $2.49 file?
Every time you fill the tank, file the chain, and you'll never have to grind it.
File went up to $3.49, I've got one. Used it last Friday...(and I don't even have a woods, but I do have a woodstove.)