I bought 2 this year and learned a few things although neither were led.
I realize this may be impossible to tell buy just looking at one in a store but... some things I learned is to look at how it actually clamps to the book or magazine. Because the clamp may only be enough for x number of pages and you may not be able to actually clamp it to the book cover, then it will have to be adjusted every 2 pages. If its a little heavy it can drag down the pages, especially if it takes 3-4 aa batteries. Look what kind of adjustment is available because some may have to be adjusted every so many paragraphs. Also the brightness level could reflect on certain kinds of paper for example glossy paper in a magazine. I also perfer to use a headlamp, but if you get a headlamp instead, remember that the ones with battery packs which go at the back of the head will be uncomfortable when reading while using a pillow in bed or a lazyboy recliner.
Because of this my booklights are now used as backup night lights.