Mikhail - not much comparison between a Glowring X2 and a Glo-toob. I have an X2 (green), and it emits enough light that you can find it in a dark room. In a pitch dark room, it puts out enough light that I can read about 2 lines of text if I lay it down on the page. If I were dark adapted, I could probably see more. So, you can see it, but it doesn't really kick out a circle of light.
The Glo-toob, on low, is much brighter. Puts out a circle of light - I could see the floor in about a 3-foot circle as I held it in my bathroom. I could have read a magazine by its light. And on high - well, it's a lot brighter than that. That said, it's still not a flashlight - maybe it's a weak, tiny lamp? In the end, as with the X2, it's designed to be seen, not to see with.
I don't have a Krill, so I can't compare - sorry.
Dave