First thought: this continues to be an interesting 'real world' study!
Second (tractor automation) thought: yep, I really don't like expert devices that do their own thing without providing full status info as to what they are doing and why.
My own inclination would be your second option, but mainly because I have a long term low maintenance attitude: a resistive test load of some sort could be simple, robust, and would last indefinitely.
On the other hand, a light meter, while probably requiring shelter from the elements, and periodic cleaning, would yield more data.
The perfect fix would be a CC that also delivered rich raw status info.............