Very good illumination in a small package, but turns on in my pocket because of button design.
"I used to carry a Rovyvon A23 at 1000lm as my EDC, but switched to the T4K because I liked the 4000lm in a similarly sized light. However, twice now I've gone to use the T4K and found it dead and I found out why. They both have a side pushbutton but Rovyvon has a ring around theirs, whereas the Nitecore's buttons just stick out. On top of that, even though you can lock out the T4K, one of the buttons can override the lockout and go to high mode. The flashlight was going on in my pocket when pressed against other things, like a comb, in high mode and sometimes I wouldn't know it, sometimes I felt it burning my leg. This is the only drawback. If you have a bag, or backpack, or anything else that won't push the button by accident, it is fine for edc, but I may try to epoxy a metal fence around the button on the side"
