Comix is just an image viewer that has been optimised for comic book reading. An eReader is more like a PDF reader but designed for reading books, News papers and magazines on tablets and PC's.
At the moment its still a pretty new technology but will be something as common as mp3s soon. At the moment they are dealing with the same problems as mp3s did when it was first introduced. I do believe that Kobo will be the ones that will come out on top. They do want an open standard for eBooks and eReaders. There app for smart phones do have the ability to import ePub or PDF files but the Linux desktop version hasn't got this feature yet.
You can read more about Kobo here:
http://tinyurl.com/2wob62yhttp://tinyurl.com/2utpfqfhttp://tinyurl.com/24sm8thBut for now I think the best option to go for is
calibre, its already in the repo so all you need to install it is:
sudo apt-get install calibreHere's a Video of what it can do.
One feature that I do really like a lot with calibre is the ability to download the news from your favourite News outlet and it will turn it into a News paper for you.