Good question :)
The actual step-down is noticeable as a 0.5sec long "flicker". But interestingly i could never distinguish the brightness levels before vs. after it. To me, in all honesty and sincerity, both levels look equally bright.
On the D25A clicky Ti xp-g2 however the levels before and after were very far spaced apart. Huge brightness drop. This resulted in continuous runtimes of ~5.0hrs on Turbo-mode (Eneloop) :D
Please shoot if you have more questions about TX or Alison ;)