This is a light weight single AA XP-G headlamp with a high of 195 lumens and a low of .2 lumens and it has a frosty lens and thus the (f) desgination.
It uses an electronic switch rather than mechanical and has a rather complicated but intuitive user interface. One quick click will get you to high. Two clicks are for medium and three for low. You can also just hold the button for a moment and it will go directly to low. If you keep holding it will cycle from low to high.
Each of the 3 levels (hi/med/lo) has a sub-level. When you are in the main level and double-click you reach the sub-level which just gives you another option for that level.
On high you have 195 lumens or 95 lumens for the sub-level. Medium is 28 lumens and 7 lumens for the sub-level. Low is 2.4 lumens and .2 lumens for the sub-level.
If you don't want any parasitic drain from the electronic switch or if you want to lock the button out to prevent accidental switching a slight loosening of the tail cap will do the job.
The beam adjustment angle is simple...just reach up and rotate (twist) the light about its horizontal axis in its headband holder. It's held by two silicone loops. This headlamp is an angle light so there is a tube with the head at 90 degrees from that tube.
Changing the battery is easy and can easily be done in the dark...just unscrew the tail cap, pop a battery in and screw the cap back.
I like to use lithium primary batteries. The fact that this light uses AA rather than AAA means that batteries are essentially half price. AA and AAA batteries usually cost the same (and lithium batteries are relatively expensive) however one AA batteries has twice as much power as one AAA battery so you are in effect getting AA batteries for half the cost of AAA batteries.
This is a floody light but not a pure flood light. There is a reflector it just has a frosted lens over it so there is some throw but just not a defined hot spot. I've found that it works in most cases for hiking and yet it's still good around camp or for reading as there isn't that annoying hot spot in the middle.
There may be some occasions when you would like more throw. Just take a small flashlight or do as I've done and also order the H51 (without the frosty lens) and have that as a backup and just consider it as a spare battery holder :)
The headband is lighter weight than most of my other headbands for heavier headlamps so it's easy to wrap it around the headlamp for easy storage.
I especially like the two low modes in this light ...2.4 lumens and .2 lumens. The later is good for just sitting around outdoors talking to friends. The former is actually enough to move around with.
One final point. There is memory of sorts with this light. Which ever setting you've chosen at each main level will be remembered so if can remember that you chose 95 lumens rather than 195 as high the last time you were in the high mode.
It's a nice way of doing things. Chose the most commonly needed settings for hi/med/lo and it will remember those settings. However it's also nice to know that in each level all you have to do is double click to toggle between the two choices in that level.
I never set the .2 level as my low but once I'm in that level I frequently toggle to .2.
Budget lights work for me but I've found that budget headlamps don't. Budget is a relative term anymore. Zebralight is budget compared to Surefire or to some of the caving headlamps.
Edit:I have have the H51 as well as the H51f just reviewed. The H51 is the same fo the H51f except that is has a clear rather than frosted lens. This means that it is slightly brighter but the main difference is the spot beam (XP-G so good sized) and the fact that throw is greatly increased (of course). Detail in the direction that you are looking is increased and spill is still sufficient to see where you are going.
The H51 model should probably be the first choice for hikers if you are doing any hiking at night. The H51f can be used to hiking at night and is even better for use around camp or around your house/yard or for reading.
Both lights have enough output that they can be used for any activity but each is probably better at one or the other. Since these lights are so small (using only 1 AA) if I'm away from the house (hiking) I'm going to be carrying a spare battery anyway so the extra headlamp can really be considered a spare battery holder as well!