Mantano 2.5.18 works alright on InkBook (a.k.a. Boyue T61D) as long as page animations are turned off. You may want to turn off page border and bottom right navigation button to get some more screen space.
Make sure you get some nice font to read with. Droid Serif is great. (Just put it in Mantano's fonts folder on the device and create a new theme).
There are some small issues like half-invisible bookshelf menu or washed out grey colors here and there but reading ebooks is completely fine.
Instapaper is OK as long as you turn pagination on (it makes page-turning animation less intimidating for the device
and enable volume settings in Inkbook's settings. Pocket on the other hand is a pain to use.