I think the reason that fictionbook was not mentioned very prominently is because its not a very common format in the English Speaking world; now if you want to read Russian books, there are tons in fictionbook
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Overall, I found that converting to html2pdf to be a good solution; pdf page turns are a little slow (maybe 3/4 of a second) but since the page remains readable until it is changed, it is not hard to time the page turn so that an easy reading flow is maintained
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Bill