Hi bioskope. Astak markets and sells the EZ Reader line of ereaders. The
www.theezreader.com is a dedicated website setup by Astak purely for the EZ line of ereaders. The only difference in ordering from either site is if you're an International buyer or not (International orders are taken from Astak.com). The Bebook are sold by Endless Ideas. By purchasing from either Astak or Bebook two things to keep in mind. The price (Astak are cheaper), and secondly with the 5" reader Astak supply a protective leather cover, Bebook Mini doesn't come with one (from stylz.com they are about $25 for a compatible cover). Oh I almost forgot, the service, Astak are IMHO brilliant. They have a representative here on the forums (not officially but by his own accord) who on a regular basis listens to our concerns and wants and passes the information to and fro from Astak to us.
Now the question on 5" or 6"...it has been a popular conversation. I went through the same question prior to my purchase. Now I bought mine purely for fiction reading and find the 5" really good, the font size ranges work well. On a post in the Astak forum there was some calculation done where is was determined the 5" was 23% smaller than the 6". Here is the latest thread on 5" or 6" (
https://www.mobileread.com/forums/showthread.php?t=60365).