@Stunatra: In this case, I'd say yes, they weren't just being evil. Despite being undocumented, it was potentially a support nightmare, because it was basically implemented like the software version of a game of Jenga: and thus ended up one of the very easiest way to soft-brick a Kindle
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Embedded fonts (in KF8 files) are indeed much safer. At worst, you break the rendering of *the* book instead of bricking the device.
One of the purpose of this hack is to add a (thin) layer of safety around the process.