Depends on what you want. I looked for an android tablet with an eink thing and I figured I just needed computer glasses. Research is a really good idea. Bought a 600 dollar tablet because I thought I could use it to ink my art. Never worked for my needs, then something in the charging port got scratched and I had to watch the poor thing die over six months. I have trust issues with Lenovo.
I think the previous commenters have pretty much covered the key points. Just to add some perspective, I have both a tablet (an iPad) and an e-reader (Kindle) but my Kindle is mostly collecting dust on a shelf these days. An e-reader is better for your eyes and has longer battery life, but your options tend to be limited to the store and apps associated with the device unless you're tech savvy and willing to do the extra work to get compatible versions of works for your device. If you're looking for a device to read miscellaneous things, such as online fanfic, webnovels, manga, as well as e-books, then I'd say a tablet would be a better choice. Battery life isn't so much of a concern on a tablet if you're primarily going to be using it for reading, and you should probably rest your eyes every so often even when reading a traditional paper book. Just toggle the brightness of your screen down somewhat and you could even get one of those protective blue-tinted reading glasses if you're really concerned about your eyes.