@GregoryP: What I meant was that there seems to be rooms for improvement still, having tried other apps like Kindle, Kobo, Aldiko, Moon+, ezPDF and some others before.
In particular, there's a noticeable delay for the menu to pop up after text selection by long-clicking.
Besides, most, if not all, operations under PDF mode are (understandably) slower than that in EPUB. For instance, zooming and selecting text inside a guidebook PDF file (2.21MB, 25 pages) are noticeable slow.
However, your team's quick responses and attention (together with the expiration of the trial period...) have swung me to purchase the app. Please keep on improving the app.
(Evaluated Aldiko and Moon+ before, but they don't seem to handle annotations as well as Mantano, the ability to sync with desktop ADE is a major selling point to me...)
Lastly, please consider adding more layout customization for EPUB, like background colour, font type, size and line spacing. Text reflow for PDF could be useful too. And the interface is kind of confusing, maybe you can consolidate the various highlight and text selection options under a single item...