In general, the idea that blue light (or white-ish LED light to be most specific) can cause sleep disturbances seems to be fairly well established, from what I know. The causal mechanism is activation of certain cells in the eye that are used in part to set our circadian rhythm. (On a related note, morning daylight is especially useful for regulating our circadian rhythm, and we probably don’t get enough of it.)
The blue light myth has more to do with the alleged connection between blue lights and eye fatigue. It’s alleged that the reason computers and phones cause eye fatigue is because of blue light (and therefore, computer glasses and blue light filter lenses*), but the truth seems to be that the reason computers and phones tire your eyes is that you’re focusing on something at a fixed focal distance. (In other words, it’s the eye muscle equivalent of holding a 20 pound dumbbell with your arm parallel to the ground for hours on end. 20 pounds isn’t much weight for most people, but your arm’s definitely going to get tired from you keeping your muscles continuously contracted.) It’s probably best to take some time each hour (maybe when your Apple Watch goes off at 10 til the hour, telling you to stand) to get up, and look at stuff other than the computer. Try to look out the window for a bit, or something like that.
All that aside, e-ink is VERY print-like. If you favor reading physical (over an LCD or LED display) but want to take advantage of digital storage’s ability to carry loads of reading material, e-ink is a great option. The primary weaknesses are color and refresh rate, the primary benefits are longer battery life than LCD or LED and more print like text. I personally like e-ink for a tablet device (and I very much like to have single purpose devices, I have a MiniDisc Walkman as well as an Android based net Walkman, I have an e-ink tablet, and I have an internet radio in lieu of using something like TuneIn or Radio Garden) and don’t have an iPad at present, but I’ve used an iPad for great effect for productivity in the past and am planning on buying another one sometime in the future. I probably will choose to be pretty picky about the apps I put on it, though (to try to make it into as much of a single purpose device as possible). One thing that’ll be great (that I currently do on my iPhone less optimally) is creating templates for my e-ink ebook reader in OmniGraffle, and the bigger screen makes OmniFocus easier to use.
