Interesting that Zebralight quote this for the H51 "The 200, 140, 30, 8 and 2.5 Lumen output levels are current regulated. The 100 and 0.2 Lumen output levels are PWM generated", but that for the H31, no such specification is included. I wonder why.
The interface looks the same, so maybe the driver is the same, and therefore the PWM is used just as in the H51 (on the 100 and 0.2 lm outputs), but it would be nice if they confirmed it.