I copied and pasted this from another thread where I posted it earlier.
I did much research before buying my TK-41, and for the most part I really liked it................Except for the on again/off again problem with the on/off switch. The first 2 days it worked fine 95% of the time, with only a few failures, but on the 3rd day, the on/off switch got to the point that it would only work 2-3 out of 5 tries, and it would take as many as 4 clicks to get it to turn on once it finally did work. It also didnt always turn off. Some times it would click on for like 1/10 of a second, then off again. But as quickly as it got really bad, it suddenly cleared up and started working good again, for 3 days, then it was back to screwing up 2-3 out of 5 tries. So I sent it back, but I think that bad switches on the TK series lights are rare, as not many people have posted about it. I've only gotten 2 dud lights so far out of about 20, and this was one of them, so your's will probably be fine in every aspect.
My LED was perfectly centered. If not for the bad switch, I would've really liked the light. Great beam, nice tint, great throw, nice UI, etc.
The good things about the TK-41 are: It runs on AA's, which are cheap and easy to find everywhere. Its tough, has good anodizing, nice beam, nice tint, great throw for an 800 lumen light, nice UI, I like its modes, etc.
Downsides: Its heavy compared with other similar throwers, as 8 AA's are heavier than 2 -18650's. But if you choose to get an 18650 light, you will have to buy 2 of them for about $25-$35 for 2 good ones, plus at least $25 more for a good charger for them. Whereas with AA's, you can buy a 24 pack for about $7. That will fill this light 3 times! Or get Eneloop rechargeables.
If you do choose to get an 18650 thrower light with similar specs, then the Sunwayman T40CS might be a good choice. The Olight SR51 is nice, but only has 2 brightness modes with no good low mode.