jon2901323 wrote a review of Princeton Tec Apex Pro Headlamp on April 10, 2012
I purchased this headlamp specifically because it uses CR123 batteries which meant that I can share the same power as my Steripen Adventure handheld UV water sanitizer. Having to only bring one type of battery on expedition really simplifies things.
On Mt. Kilimanjaro and Mt. Kenya, I loved the fact that the headlamp will burn down every last ounce of power from it's batteries before quitting. Other headlamps will simply shut off if they don't get enough juice. This meant I could use the "dead" batteries from my Steripen for a few hours in the headlamp, which is quite economical.
In terms of performance, I had no issues. The light output is great on a full charge, though to maximize battery life, I usually kept the side-lights on (not the main bulb) and set to the lower setting. The light-weight of just two CR123 batteries is fantastic.
I would use this headlamp on most expeditions up to 8000m peaks. For 8000m and above, I'd consider taking a lamp that uses more batteries (sacrifice the weight savings) for performance under severe temperatures.