Originally Posted by NiLuJe

They did update the fonts, and they're indeed a tiiiiiiiny bit darker, and possibly sharper (better hinting bytecode).

There's a link to some real kindle screenshots comparing the two versions somewhere, but I can't get my hands on it right now.

The KT (5.1.0) is using the same version of Caecilia as the K4 4.0, NOT this updated version.

Here's a crappy screenshot of the two versions rendered by a somewhat similar font rendering engine than on the Kindle:

(4.0/5.x on the left, 4.1.0 on the right) [The commas are prettier, for example ]