So as not to slight Moon+ Reader and Aldiko, below are their upgrade options, including (in Moon+) additional fonts, background images/textures (!), annotations/highlights sharing and Dropbox integration. The price is €3.80. Aldiko Premium basically promises extended customization options and some extra functionality, for €2.49. There seems to be no premium version of FBReader.
It looks like I might later on dish out at
least the €8.36 + €3.80 for the premium versions of Mantano & Moon+ to check them out.
