LGTM!, at a minimum there should be docs on the enable flag indicating it probably needs calibration via powertop --calibrate. We shouldn't do that automatically, I think, as it can make the computer appear broken for a while :)

When looking at the man page there is no indication that calibration mode will improve effectiveness of this option:

       -c, --calibrate
              Runs powertop in calibration mode.   When  running  on  battery,
              powertop can track power consumption as well as system activity.
              When there are enough measurements, powertop can start to report
              power  estimates.   One can get more accurate estimates by using
              this option to enable a  calibration  cycle.   This  will  cycle
              through  various  display  levels  and USB device activities and
              workloads.

So my guess is, that this is only required to get more accurate measurement results from powertop.

I can take a look at the source code though.

I checked out the source and autotune defaults are more or less static:

https://github.com/fenrus75/powertop/blob/master/src/tuning/tuning.cpp#L323