The 50/50 acetone/ATF mix is the way i would go as well. Use one of the following, Carlube ATF-U or NAPA MV ATF and if you can't find pure acetone locally, buy some nail varnish remover that says' it pure acetone (some have oils in for the fingernails apparently) and mix in 50/50 proportion.
Shake well in a sealed container then brush, dribble or spray on and leave to soak, repeat a few times overnight with another dose shortly before trying to shift it.
Make sure you keep the container sealed to prevent the acetone evaporating and shake before each use as they two separate easily. With this mix, it will eventually shift.
If using any sort of tool with a movable jaw (locking wrench as you linked to, adjustable spanner etc) make sure the movable jaw is in the leading position for turning as it reduces slip and increases grip. For example, an adjustable spanner trying to undo (anticlockwise as viewed) a nut, the movable jaw will be underneath the nut and the fixed jaw above the nut as you look at it. As you try to turn the nut anticlockwise, the handle will help push the movable jaw onto the nut. Same goes for Mole Grips, Vise Grips, the Irwin Grips you linked to and so on.
*** EDIT *** This YT video puts my words into (not very) pretty moving pictures :
https://youtu.be/qsHomDTTRXo