Body: The first thing that I immediately noticed about the battery tube is the thickness of its wall. The TK20 may well have the toughest battery tube of any flashlight I've seen, with a wall about 3mm thick. For grip, Fenix decided to go with a rubber sleeve with a wave texture over the battery tube instead of traditional knurling. This rubber sleeve provides improved friction over a knurled metal surface especially when the light is wet, or if you have sweaty palms. However, one thing I didn't like about this rubber sleeve is that it isn't fitted tightly around the battery tube and is able to twisted around rather easily. Threads on either ends are well machined with a rubber o-ring placed on either ends as a seal against moisture. The threads on the rear are anodized so the light can be locked-out by loosening the tail cap to prevent accidental activation. There's a slightly raised lip at the front end of the battery tube with two screw holes, this is where you may attach the included clip with hex screws. The screw holes don't go all the way through the wall of the battery tube so there's no worry of water seeping in even if you don't attach the clip. The tail cap has a simple and functional design, its rear end is scalloped to that it would be easy to engage the switch while still allowing the light to tail stand quite stably. There are 2 wide slots for lanyard attachments as well. The TK20 uses a forward push button so momentary activation is possible. It has an average amount of tension and travel, and also provides a positive tactile feedback when clicked

Bezel/Head: The battery tube maintains a fairly clean look, with the addition of a removable grip ring which also serves as an anti-roll feature. After unscrewing the grip ring, it can be a tight squeeze to slip it out due to the rubber o-ring at the tail end. There's a band of diamond textured knurling about 3cm wide, and two flat surfaces machined on with the Fenix branding printed on it. The clip on the TK10 is nice change from the T1 as it is attached to the battery tube instead of the head so it won't scratch against the battery tube when twisting the head for switching between modes. The clip is also removable now via 2 hex screws. A hex key is included in the package, however I did have problems removing the hex screws. The hex key is slightly too small for the screws themselves and I wasn't able to unscrew them because it kept slipping out. The TK10 has great ergonomics, it feels really comfortable and secure in hand with a hefty mass. The wall of the battery tube is very thick, I'm confident that it can handle rugged abuse. Its internal diameter is wide enough to accommodate protected 16340 cells easily. Threads on either ends of the battery tube are very well done, smooth and thick. Head and tail cap screw on very easily without any cross-threading or grinding, very nice. There are thick rubber o-rings which came generously lubricated. These serve are water seals, 2 at the front end and 1 at the rear end. The TK10 is advertised as meeting IPX-8 waterproof standards, although maximum submersion depth wasn't specified by the manufacturer. Type 3 anodized coating on its exterior surface is smooth and consistent throughout.

The tail cap now has a hand of knurling for grip instead of scallops like the T1. At the rear end the tail cap has a deep 4-point scallop machined into it, one of the points has a hole for lanyard or key ring attachments. This design allows for easy switch activation while still allowing the light to tail stand on flat surfaces. The rubber switch cap has a checkered texture and feels quite thick. The switch module housed in the tail cap is a forward push button, allowing for momentary activation which I personally think is a must-have for tactical flashlights. The switch has a noticeably longer travel than other Fenix products which use reverse push buttons. Clicking on the switch provides good tactile feedback and audible click. Switching mechanism is responsive so signaling with the TK10 poses no problems.

Output: The TK10 is pretty straight forward feature-wise when compared to their recent series of products which may have up to 6 modes, identical to the T1. This light has a simple and easy to use general/turbo modes suitable for most situations. Switching between output levels is done by twisting the head. Tighten for turbo, loosen for general.

The beam profile of the T1 produces a narrow spot with a fairly bright spill beam as well. Its also smooth and artifact free thanks to its textured reflector. There is however the dark ring around the hot spot which is common in most lights using the Cree XR-E emitter. Also, the emitter and reflector are slightly misaligned on my sample which results is a slightly skewed corona around the hotspot, not very noticeable. This might also be the reason why my TK10 seems to output slightly lower lux numbers compared to the T1. The beam's color temperature seems slightly cool on my sample. Runtime is above average considering its output, and regulation is very well maintained as characteristic of most Fenix products. When compared to the T1, the TK10 regulated output isn't as tight as the T1 as can be seen from the slightly sloping runtime graph. To be fair it is a very slight slope and doesn't make any difference in practical use, also the runtime is slightly longer over the T1 on both Turbo and General modes. As you can see from the gallery below, the TK10 uses the same "B02A" circuit as the T1 so these differences could be attributed to factors such as LED binning and thermal management on the TK10 vs T1. The TK10 is designed to run on either 2x CR123 or 2x 16340 cells, once the batteries start to run down and fail to maintain regulation, the light will start to pulse rapidly as an indicator for a battery change. You may also use 1x 17670 cell in the TK10, but it only works on Regular mode as the 3.7V from a single 17670 cell will cause the low voltage warning to trigger on Turbo mode as can be seen from the graph below.

Runtime:

Switch: The switch is a rubber covered clickie and is fully recessed in the tailcap which allows the light to stand on end and be used as an electric candle. Despite the fact that the switch is recessed, it is very easy to use. Click on, click off. You can lock-out the switch by unscrewing the tailcap 1/2 turn. This will prevent accidental activation when packing the light in your backpack or luggage.

Batteries: For batteries, this light is approved by the manufacturer for use with one 17670 1600mAh, two 16340 750mAh or two CR123 batteries

To change out the batteries: unscrew the tailcap, drop out the old cells, place in new cells observing proper polarity. Reattach the tailcap and you're ready to go.

Accessories: Several accessories are included with the light. Inside the package you will find a Nylon wrist strap, Spare rubber switch cap, Spare rubber o-rings, Key ring and a Braided nylon lanyard. The Fenix brand is one of the few I have received that included this many accessories, and I have never seen a light include a spare rubber switch cover.

Picky Little Things:Nohing to report

Conclusions: The Good - Solid build quality and cleanly machined. Nicely designed anti-roll surfaces and grip ring which work well. Comfortable ergonomics. Tactile and responsive switch. The Bad - Tiny hex screws seem impossible to remove with the included hex key. The Relative - Slightly cool beam tint. Uses a forward push button which allows for momentary activation. Detachable clip designed for head-up carry.

Quick Facts Table: