I had a 3rd gen X1 from last summer - loved it. Added a dimmer black 2nd gen in Jan (Target - old stock!) - and another 3rd gen Friday - closeout $14. I did this because my original 3rd gen had mysteriously lost it's greater brightness - yet retained it's high, and varying, current draw. I was prepared to send that original one back to Inova - even have a RMA for same. I elected to compare the newest and oldest - opened a fresh pack of alkaline Rayovac AAs... oops! They were equivalent! I tested my open pack - 1.35-1.38V - the fresh pack was 1.60-1.61V. The open pack were 'pullouts' from a roboT! Check your batteries - the newest X1 seems to lose regulation below 1.35V - perhaps the pulsing some have noted. I haven't tried them on NiMH yet - maybe not a great idea. Lithiums, at 1.75V, may not be the answer, either... but lifespan would likely be ~6 hr at full brightness.
I guess, despite it's AA appetite, I prefer the current version - a steal at 'closeout' price... and a decent buy at it's regular $20 - especially for a well-made, and made in the USA, flashlite for the pocket or purse.
John