I too have the A5IT and am using Fbreader 0.56. I have also used Aldiko, v. 1.12 - either works well and each has its pros and cons. Calibre doesn't detect either so I just download ePubs to a micro SD card and readthem into my A5IT I find it a pleasure. Either reader is freeware.

Outside of the short battery life (I get about eight hours), the device has HD 4.8" screen, large # of fonts, easy page turns and full color (images are very good).

Books are stored either internally or on SD card.