I use KOReader with Koobo Clara BW (300 ppi screen), it's great.
I still have to remove a lot of CSS from most books before uploading, but after that, it is very good, as you can fine-tune every aspect and have every book look similar. Which, in my opinion, is necessary because e-ink readers still don't have enough resolution to use all the fancy fonts authors may have thought. Also, the ability to set margins to the same is very important to me.