I gave BookFusion a shot this afternoon, despite some leeriness around the whole "entirely cloud-based, no option for account-free local use". Results were mixed.
On the one hand, it did better than expected on all the English books I tested it with. The scrolling worked, the tables of contents all displayed correctly (and even had percentage indicators by each entry, which were a nice feature that had never previously occurred to me as something to want), inline images displayed correctly (another thing Marvin is not very good at), overall I failed to find any flaws of note. On the whole, then, I'm pretty impressed with it for reading English books with horizontal text.
On the other hand, when I tried it with a Japanese book with vertical text, the book was thoroughly unreadable. The reader only let me scroll vertically, not horizontally, so each chapter was truncated down to just the first few lines, impossible to read the rest of (since scrolling down would instead take me to the next chapter). Moreover, the text which
was visible was being displayed upside down, written bottom-to-top instead of top-to-bottom, with no option I could find to flip it into the correct arrangement.
And, on top of that, the one image visible in one of the chapters I checked was truncated, with its top section cut off from display.
(
Here are a few screenshots, comparing the book's thoroughly-incorrect display in BookFusion with its correct display in Yomu, in case the images are a helpful supplement to my description for debugging purposes.)
Overall, I was impressed enough with the handling of the English books that, if you ever release a non-cloud-dependent version of your reader, it's pretty plausible that I'll end up switching to it as my main reader for English books. However, the poor handling of Japanese books prevents it from being the complete all-in-one reader I was hoping it would be, and means that I'm still stuck with Yomu as the best reader I've found in the vertical-text-display field for the time being.