The e-ink reader screen is designed for reading in normal lighting - it does not have a back light. That is the main reason I use it - to read manuals in bright sunlight. There are various lights that you can attach to the USB port that will allow you to read in the dark.
The LCD screen is 1024x600 which is most probably different to your iPad resolution. This might make it appear grainy but I find nothing wrong with mine - OK, I'm comparing it with a 28" 1920x1200 monitor.