Rating: 4 / 5
the H50-Q5 has so many pros:
1. very small size (one of the benefits of being a "twisty".
)- just slightly larger than the cell that powers it (1xAA - alkaline, NiMH, or Li-Primary; it can also be powered by a rechargeable 14500 Li-ion cell, but low and med will be the same and hi will be lower according to one website indicating that the light isn't running in direct drive with a Li-ion cell, otherwise it would be initially brighter running off of the 3.7 to 4.2 VDC of the Li-ion cell; of course, burntimes will be significantly shorter on the 14500 cell).
2. very light
3. long burntimes on the 1xAA cell (other than on HIGH o.p. mode)
4. nice flood of light o.p. with a 120deg pattern.
1. essentially no throw since it lacks a reflector or optics (know this "going in", so that you aren't disappointed). as such, it will work better when backpacking "indoors" where there are many vertical and/or flat surfaces to reflect the light back to the eye.
2. could wish for a setting midway b/t HIGH and MED.
3. lack of throw makes picking out faded blazes on rocks and trees difficult until one is closer than this reviewer prefers (of course, this reviewer's age degraded low light vision may bear a portion of the blame; younger users may not have this objection).
4. if used in a fashion other than headlamp mode (e.g. clipped to packstrap or waistbelt, or shirt collar/crew-neck, etc.), i need to cut a small piece of plastic to insert under the top of the rubber hood to control light from spilling up towards my eyes. not absolutely mandatory, but this did prove helpful to me, at least.
the now recently released, recently recalled due to UI bugs, and now more recently re-released H30-Q5, hopefully with the UI bugs worked out (using a single CR123A battery - which in some applications makes finding replacement batteries more difficult) is brighter with a narrower 80deg pattern, and burns slightly longer. plus, for those who prefer such, the H30 is a "clickie" and not a "twisty". the H30 is shorter and bulkier (sorta' like this reviewer) than the H50, but otherwise shares much in common with it's taller predecessor.
i find this lil' light's flood pattern makes for a nice "fill in" light when worn at chest or waist level and coupled with a head mounted (via JakStrap) flashlight (pick any Fenix flashlight you prefer) which has a tighter beam for more throw.
all in all, the H50-Q5 light is unique as far as this reviewer's knowledge of headlamps is concerned. definitely worth a "look-see", IMO.