Re Battery Whipper
I'm using 2.4mm on all residential and 2.7 on this one huge fortnightly Commercial job that my app shows I walk 7.5kms. Small commercial jobs use the 2.4
All jobs are vertical edged as I have it down pat over the years and Green Trail Blazer is used.
Use a separate dedicated spool and circular end base for the 2.7 line as the line wears a different slot in the aluminium exit fitting, also the 2.7mm wears a bigger hole in the spool grooves.
Standard Guard used, but bite my lips tightly closed more often in feral use situations or anything other than good lawns. Also ensure the protective glasses are properly on face, so no Johnny Howard eyebrows. Not the best guard, well not as good as the petrol unit guards.