I could see 12 thou being a bit much for the Emery.
I measured my out of round drum at 5 thou variation.
With 5 minutes of work I could feel the contact area getting greater.
The whole operation took perhaps an hour, which doesn't seem much to fix a problem, without having to start the car or leave the shop.
And with just 5 thou out of round the low speed pulsation was really harsh, so it doesn't take much to make bad ( or good) braking.
Glen