The SC21 is Sofirn’s first 16340 light if I’m not mistaken, and it’s a nice one! I’ve used the SC31pro with a shorty tube (ie, to use the half-length 18350 instead of 18650 cell), and it’s a surprising little powerhouse, and the SC21 is even smaller/thinner than that.
It comes as a kit, with the included cell, in a thin but nice small light-brown cardboard box, not the fancier black’n’blue boxes as before, but it’s more than adequate, as without the plastic tray, etc., you get a nice compact package.
In the box is the light with included cell (remove the insulation disc before using!), the usb-C charging cable, snap-on clip, and a baggie with useful goodies like a lanyard and extra O-rings. Everything’s nicely Tetrissed into the box with no room to spare. 
What’s a really nice treat is that this light has it all, including usb recharging built-in. So not only is it compact, bright, and with a beautiful CT/tint, but also doesn’t need an external charger!
On first inspection, the light has typische Sofirn semigloss black anodisation, pretty much flawless with no nicks or dings or chips anywhere, not even the edges. Its rather familiar switch, black plastic ring with clear center to show the internal LED, is as mentioned a familiar sight but doesn’t protrude as much as in some other lights, and has no discernable “wiggle” or dead travel. It also seems to have just the right amount of springiness, not mushy but not hard to press, either. I don’t mind a stiff switch (and lots of times even prefer it, to prevent accidental activation) and the small protrusion might help with that.
The usb charging port opposite the switch is covered with a rubber flap that takes a devil of a time to press in thoroughly, but it ends up as quite a tight seal. And it’s usb-C, which is a fan favorite. I don’t mind micro over C, but C is what lots of people prefer, so it seems a smart choice to go with C. 
There’s a magnet in the tailcap to let it stick to ferro surfaces, too. As always, while magnets can come in very handy to stick to the hood of your car in an emergency, etc., don’t let it get near credit-cards or anything else with a magstripe, as to not corrupt/erase the embedded data. The magnet’s not exactly a powerhouse, but works fine to hold the light to flat surfaces. Rounded surfaces like pipes are more problematic.
Despite the magnetic tail (usually flat), there’s still a ridge with holes to be able to attach a lanyard, if you prefer. It also explains why the magnet inside is likely a smaller diameter than what could fill the entire tail.
The front glass is crystal clear and seems uncoated. The reflector is a nice mild orange-peel and blends the beam nicely. Knurling on the battery-tube is grippy without “biting”. There are some fins around the head to help shed heat. All in all, everything looks quite good.
The emitter is an LH351 all right, but seems to be a B instead of a D as listed. No matter, as it has the same wonderful beam I’m used to. And the listing says it’s 5000K, but seems to be a much sweeter warmer color, more like 4000K instead. Color me very happy!
The beam itself has few if any artifacts, and is nice and floody, with a gentle transition from hotspot to spill thanks to the OP reflector. Not a hint of any “fried egg” beam (ie, yellower in the hotspot vs spill). Everything’s nice and even throughout, even when “white-wall hunting”.
The UI (user interface) is nice and simple, yet very useful. Click on/off. Hold when on to advance modes. Press’n’hold from off to get to moonlight. Double-click for turbo. Triple-click for strobe. Quad-click for lockout. When locked out, holding the button gives you momentary low light so you don’t have to unlock it for brief bursts of light. Nice!
Charging is easy, just plug it in and wait. The switch lights up red when charging, green when done.
All in all, it’s an incredible little light, and that it gets so bright even with a 16340 cell is pretty amazing. It’s certainly the brightest 16340 light I’ve seen.
