12mm spanner, not 10mm
And yes, it's about getting the correct freeplay, not just getting it where you want it.
If you have a broken pedal box, buggered hydraulic system or a poorly adjusted pedal, then it has other issues.
Don't forget that too far in the adjustment will cause just as many problems as not enough adjustment so only make small adjustments ie: 1 rotation of the rod, so that you don't go too far before it's too late