I bought two of these during this year's Black Friday sales event, and as soon as I received them and played with them for a day, came back to buy two more to stash in toolkits and glove boxes.

The advancement in LED lighting and battery technologies has really led to some stunningly efficient modern lights, and the Jetbeam KO-01 is one of them. I've got old school 5D- and 6D-cell Maglites with the single LED TerraLux conversion, and the KO-01 (in the middle two settings) is brighter than the Maglites (not surprising, as the conversion is rated at 140 lumens), has a better beam pattern, weighs about 1/10 of the Maglites and runs longer to boot. In the highest setting, the KO-01 beam is competitive with winter sunshine, and easily overpowers typical indoor lighting. In the lowest setting, the KO-01 seems practical for use without waking nearby sleepers, about like a strong nightlight; the specs claim 1 lumen in the lowest setting, but it must be substantially more powerful than that. I'd guess more like 20 lumens. Overall, the four brightness settings are very usefully spaced. For any purpose except baton work, this little Jetbeam is clearly superior to the Maglites. It should go without saying that the KO-01 is also superior to CR123-powered LED lights of even just a couple years earlier.

The KO-01 has a really deep fixed-focus parabolic reflector that provides a nice uniform spot with a well-defined larger outer area. I think (but have not tried taking it apart to verify) that the front lens also has some optical properties other than "flat cover glass". The outer area is not as broad as the Maglite outer area and has substantially more usable light in it. Color is reasonably good with a slight yellow tinge to the central spot and a blue tinge to the periphery of the outer area of the beam. Overall, it's a "daylight" white, and much nicer than the heavy blue color of lights from a few years back.

Design and construction seem very well done. The head, the body and the tail are separate machined aluminum pieces, with the threaded joints sealed with O-rings. The rings came pre-greased, which is a nice sign. It's quite sturdy without being the least bit clunky. Easy to hold with effective no-roll machining for when you set it down. Tail stands nicely. Intelligent (if trivial) provision for a lanyard which won't interfere with tail standing.

The one head-side button has a sensible control pattern for cycling through settings, with last-setting recall from off. You need to hold the button for about 1/2 second to turn it on or off, a momentary "click" won't do. When on, a click cycles through the settings, When off, a click does nothing. You won't like this light if you require a tail-end button.

The USB recharging feature for 18650 batteries seems to work just fine. The power-indicator (hidden behind the button) also indicates when the battery is recharging and goes out when it's done.

The one feature that I don't think was done very well is the strobe, which is far too fast. It's fast enough to be called a flicker, and would be much more effective at dazing someone or for signalling if it were substantially slowed down.

Other than some very minor stylistic differences, I don't know what the difference is between the Jetbeam KO-01 and Jetbeam DC-R20. From the published specs, they look equivalent, although perhaps they use different Cree LEDs? KO-01 is currently $20 cheaper.

I'm an EMT on the night shift so my flashlight is an important piece of equipment. I chose this JETBeam KO-01 for its very broad range of output as well as the long life of the rechargeable 18650 battery. I've had multi function lights before and didn't like how I had to cycle through every power setting to get to the one I needed. This JETBeam model remembers the last setting while also providing a very easy short cut to get to its brightest output. In my work, I prefer to start with the lowest output since I may be inside a darkened bedroom or right in front of my patient. But if I'm outdoors, I may be managing patient care, wrangling the stretcher etc. so I want an easy way to get to my brightest output without a bunch of fiddling around. A quick "double tap" on the power switch takes the light from it's previous setting (in my case, the lowest) to the "turbo" setting. Very handy!

FYI: I realize that the marketing people needed over 1,000 lumens for bragging rights but really, the 240 lumens setting is more than enough for me.

Engaging the strobe is also quick and simple: Once in the "turbo" mode, another double tap and you have a disorienting tactical strobe (or a great way to get the attention of other responders on a scene).

I was pleasantly surprised at how much I would appreciate the recharge function. If I use my light quite a bit on a scene, I just "top it off" with my cell phone charger when I get back into the ambulance. It charges pretty quickly.

I would have gone 5 stars on this one but the power switch has two drawbacks: 1. It can turn on while in my pocket and 2. Good luck finding the power switch if you're wearing cold weather gloves. I plan to add a pair of "bumps" on either side of the switch using JB Weld. This should prevent pocket activation as well as give me a tactile location of the switch without me having to look at it.

Besides a more tactile control switch, I would love to have a beam focus option for spot lighting but that's not a deal breaker. This light could also benefit from a clip so I could hang it on my shirt or ball cap but again, that's not a deal breaker.

The light's construction and quality of beam are fine.

However, I'm just not getting used to the user interface - and have to struggle with multiple button presses *and presses of different lengths of time* to get what I want.

It's like have one car where the break is on the right and the gas is on the right. I almost wince when needing to use the light, knowing it's just not going to do what I want without fiddling for ten to twenty seconds. I've never had that issues with a couple other flashlights I own, each with their own interface.

In the month I've had it, the light has also come on in my pocket twice. And I worry about the longevity of the rubber flap that protects the on board USB charging port. Time will tell if if holds up, or if that port will begin to leak, corrode, etc... With the rarity of charging in these great batteries I'd rather the port it was less convenient, and a bit more protected.

Overall, I don't recommend. if' i'd bought locally, I would have returned it due to the interface that just doesn't do it for me.

Very Bright, nice battery choices, good size to put in vehicle.