Three Portable LED Lights
All three are quite good, but there are differences which might make you prefer each over the others. All three emit white light only, and all make a constant, flicker-free beam, in addition to "strobe" and SOS patterns.
Each of these uses a single 18650 lithium-ion battery. These batteries make very bright light possible compared to AA batteries.
The Anker and Slonik both allow you to charge the battery in-unit with a micro-USB cable. The Nicron does not — you'll need an external charger.
The Anker and Slonik both include a battery. The Nicron does not.
The build quality on all three units is excellent. These are solid products.
The Slonik is a headlamp. It fits comfortably on the head with an elastic strap. It's easily adjustable to point from straight up to straight down, and it maintains its position really well, by means of a simple, reliable design. Its light pattern is a fixed medium flood with a bright spot in the middle — very versatile. The Slonik has 6 brightness levels: 100%, 75%, 50%, 25%, 10% and 5%. This light goes from VERY bright to quite dim. The dimmest level is just right for close work when you don't want to disturb others with a really bright light. At 100% it's extremely bright.
To turn it on, just click the power button. There is no "lock" feature to prevent it from turning on if bumped, but the button doesn't protrude, so accidental power-ons shouldn't be common if you are reasonably careful when you store it (it comes with a little case you can store it in, which is firm enough to prevent bumps even if you pack it tightly into your luggage).
Once on, the brightness is easily changed by pressing and holding the power button while it cycles through brightness levels. It also has three other modes: strobe, SOS, and beacon (in which it flashes at full brightness once every 3.5 seconds). These special modes are achieved by double-clicking the power button. So if you never double-click, you won't encounter them. It's simple to operate.
Perhaps the only negative about the Slonik headlamp is that it has no memory feature, which means that whenever you turn it on it always turns on at full brightness. It won't remember how bright it was set last time it was on. You'll always have to dim it if you don't want full brightness.
Anker Bolder LC90 Flashlight
If you are looking for the brightest light here (by a slight margin), it's the Anker Bolder LC90. The Anker also easily zooms nicely from a tight spot to a wide flood. Unfortunately, the Anker is also the largest of the three lights. At 6.5 inches long, with a front-end diameter of 1 and 9/16 inches, and a handle diameter just over 1 inch, it's a bit bulky to put in a pocket. It also has no belt clip, and its shape in the hand is nearly perfectly cylindrical, with shallow, mostly lengthwise ribbing, meaning it easily slips out of your grip. There is a wrist lanyard provided to help prevent this.
The Anker has a genuine, click on/click off button, which also supports momentary on/off by pressing it half-way down (and then releasing it to turn off).
The Anker has three brightness levels, plus strobe and SOS modes. That amounts to five modes which you can cycle through. The way you switch between modes is to turn the light off briefly, then turn it back on. "Briefly" means for under 7 seconds. If you leave the light off for 7 seconds or more, then turn it back on, it comes back on in the same mode. This memory of the last mode used is a nice feature, but if you don't want the light to change modes, make sure you leave it off for 7 seconds or more! I'd have preferred this duration were around 2 or 3 seconds rather than 7, because it results in more accidental mode changes than I'd like.
The Anker treats all five modes equivalently with respect to how you choose them. There's no feature to make the less-frequently used modes harder to get into. Because of this (and because of the memory feature), you'll be going through strobe and SOS modes more often than you might like.
The dimmest level on the Anker is about the same as the 50% brightness level on the Slonik headlamp. The high, medium and low levels on the Anker aren't very different from each other. I wish the Anker could go dimmer.
Nicron N9 Flashlight
The Nicron N9 has a maximum brightness between the that of the Slonik and the Anker. It has a spot with a medium flood around it, similar to the Slonik, but even tighter. It does not zoom. At 5 inches long, with a back-end cap diameter of about an inch, and a grip diameter under 15/16 of an inch, with diagonal cross-hatched ribbing, it feels very secure in the hand. It also has a firm, yet removable belt clip. I don't see any reason to remove the clip. It's unobtrusive.
The Nicron has a magnetic back-end cap, allowing it to be mounted to most things made of steel. It also has oblique swiveling head, allowing the light to come straight out of the Nicron, or in a direction perpendicular to its body, or any angle in-between. The combination of the swiveling head with the magnetic back-end cap means that given a flat steel surface to mount the Nicron to, you can easily point the light in any direction away from that surface.
The power button of the Nicron is on its side, positioned for thumb use. To turn it on, you must press and hold the button for half a second. To turn it off, you must do the same. This means a single accidental bump of the button won't turn on the light.
Once the light is on, you adjust its brightness simply by clicking the button. There are four brightness levels, each quite distinct from the others, and the dimmest setting is about the same as the dimmest setting of the Slonik. It's a wide brightness range, nicely covered by the four different levels. By comparison, the Slonik may have too many brightness levels (six), and the Anker may have too few levels (three). The Nicron really hits a sweet spot on this.
To get to the strobe mode (from any other mode, off or on) on the Nicron, you simply hold the button down for a little over 1 second. Once in that mode, to enter SOS mode, you just click the button once. From SOS mode, clicking the button will turn the light off. In this way, the unusual modes of the light are kept out of your way unless you do something special.
Finally, the Nicron also has memory of the last brightness you selected. Whenever you turn on the light, it will return to its prior brightness level (not including strobe and SOS modes).
The Nicron N9 is a superior flashlight, in virtually all of its design features. One negative I see is also one of its features: the magnetic end-cap. While this flashlight is perfectly sized for belt or pocket carry, you'll have to be careful to keep it away from the magnetic stripes of your credit cards! It would also be nice if the Nicron could be used to charge batteries, but I'm willing to pass that up considering how well it does everything else.
The Nicron N9 is a great flashlight. The Slonik is a great headlamp. Part of what makes both of these lights great is that they make the special modes like strobe and SOS harder to get to than the normal constant-on mode. It's also true that each of these lights has a great physical design. The Anker Bolder LC90, while having a brighter beam, and a solid zoom feature, has only three brightness levels which don't cover a wide range, and brightness selection is impaired by treating the special modes as equally important. The Anker also is a bit big for pocket carry, and it needs deeper, non-lengthwise ribbing to improve grip. As well, a back-end cap with a diameter larger than the main grip would make the light more secure in my hand.
I highly recommend the Nicron N9 and the Slonik.