Most reviews, such as the excellent comparison tests at Backpacking Light and FlashlightReviews.com, cover the earlier Princeton Tec Apex, which uses four AA batteries and weighs two ounces more than the Apex Pro - but is otherwise the same headlamp. The thorough tests at BackpackGearTest.org also cover the Apex headlamp. Outside magazine's 2007 gear guide covers the newer Apex Pro, as do detailed owner-written reviews at REI.com.
Reviews give the waterproof Princeton Tec Apex Pro headlamp top marks for versatility because it can throw an extremely bright spotlight as far as 280 feet, then switch to a wide flood beam for task lighting. Battery life is excellent, and a voltage regulator keeps the light consistent as the CR123 lithium-ion batteries fade. A strobe option is available for alerting rescuers. The tradeoff for this much light and versatility is the heavier weight of 6.1 ounces. If you don't need this much light, reviews recommend the less expensive 1-watt LED Princeton Tec Eos (*est. $40).
This comparison review tests the earlier, heavier Princeton Tec Apex headlamp, finding it the brightest of the ten LED headlamps tested. The review rates each headlamp on eleven factors - including battery life, beam quality, comfort and value.
Review: State of the Market Report: LED Headlamps (2007), Rick Dreher, Mar. 2007
This review site specializes more in handheld flashlights but also tests and rates headlamps, giving the earlier Princeton Tec Apex top ranking as the best headlamp. A separate single-product review provides plenty of detail on light output, runtime and ease of use.
Review: "Top Picks" - Headlamps, Doug Pribis, June 2007
A few owners review the Apex Pro headlamp here, giving it mostly high ratings. The staff's description also reports hours of battery life at high and low light levels, beam throw in meters plus the amount of light at two meters - the distance most important in seeing a path right ahead of you.
Review: Apex Pro Reviews, REI.com editors and contributors
4. Backpack Gear Test
Three experienced backpackers and product testers provide thorough, detailed reviews of the older Princeton Tec Apex headlamp. These reviews are especially useful because they report on field tests over a longer period than most reviews cover. One reviewer jokes that one of the drawbacks is how hard it is to get the headlamp back from anyone who borrows it.
Review: Princeton Tec Apex Pro, Reviewers for BackpackGearTest.org
5. Outside Magazine
Based on field testing, the 2007 issue of the Outside magazine Buyer's Guide recommends the Princeton Tec Apex Pro along with five other headlamps. The brief review praises the long runtime provided by the CR123 batteries but notes that this makes for one more type of battery to remember.
Review: 2007 Buyer's Guide: Princeton Tec Apex Pro, Sam Moulton, May 2007