To play devil's advocate, IPA coverage is a bit of a PITA to get right ;p.
(e.g., you can either put the blame of the publisher's side for embedding a font with insufficient coverage; or the reading system's for failing to provide adequate fallback mechanisms and fonts).
We just happen to have two or three contributors that happen to be familiar with the field in KOReader

. (We seem to attract linguistics nerds ;p).