Thank you pdurrant. I agree with your recent posts above.
Continuing the discussion of KFX...
KF8 (aka AZW3) is a particularly good format for conversion and archival because little is lost when an EPUB is converted to KF8 by kindlegen. File names and directory organization are not retained, but HTML and CSS content is. Using the kindleunpack tool, you can unpack a KF8 to an EPUB that is pretty close to what the publisher provided to Amazon originally. Because of this, I consider KF8 to be the best Amazon format for conversion and archival.
KFX is basically a binary representation of the formatting information conveyed in the source format, designed for quick rendering on devices with limited CPU power. This allows added functionality that might not otherwise be possible on Kindles without impacting performance.
Extraneous information is removed in the production of KFX. CSS styles are flattened and class names are lost. (The result is similar to that obtained by doing a format conversion in calibre.) In addition a number of heuristics are applied intended to improve the look of rendered pages. For example, large vertical spacing is tightened. These changes do not represent the loss anything that is important to actually being able to read the book. Conversion to the old MOBI format results in much more formatting loss than conversion to KFX.
At this point there are no publicly available tools to remove KFX DRM and convert it to other formats. I have been working on a KFX to EPUB converter for my own use. (Example
here.) Producing a tool for the removal of KFX DRM could lead to legal issues due to the DMCA in the US so I am unwilling to undertake that. (The DMCA is something that I believe to be worthy of protest, not KFX.)