Almost 4 years ago, I started using the Mighty Bright Xtraflex 2 on my 1st kindle and on books. I've tried several others, including the kandle (when there was a 2-for sale), the Verso-like light that Barnes & Noble sells, and I have the lighted case for my K4 (2011 kindle). I keep going back to the MB Xtraflex 2, even though I have to replace the 3 batteries every 2-3 weeks. For me it gives the most even light (and the most light).
The K4 Amazon lighted case is OK, but it's not as even as the MB and doesn't give as much light. If I'm reading and the kindle goes just a little forward, the light shines in my eyes. I still use it occasionally.
I bought a 25-pack of flat batteries for the Kandle, but after I didn't use it for a while and went back to it (a year after purchase), the bulbs died, so I've given up on those two kandles.
The B&N (Verso?) light is fine but doesn't give as much light as the MB. I bought it because I thought I could take it out with me (the MB turns itself on in my bag), but it also turns itself on in my bag.
I keep going back to the MB Xtraflex 2. It's fine for at-home reading, but I don't take it out. It would be nice to have a very satisfactory built-in light. I didn't care much for the Nook with Glowlight that I tried in a store.
I was looking forward to the KPW for the light and other features (although I like page-turn buttons), but I'm going to wait and see if the problems are fixed. Might buy one after the new year or wait for the next generation. Think I'm going to buy the K4B, based on Blossom's and other recommendations on these forums. I'm doing fine with my K4(S) for now.