[Antinoos]

But it's still true that you'll lose the ability of using Kindlets (active document files *.azw2) with 7th and 8th generation Kindles (like PW3, KV, KT3) as an alternative to start apps via KUAL after upgrading to any fw 5.9.x.

And I like it very much to start my favorite eReader software Vlasovsoft's Cool Reader directly from the library (to be more precise: from a local collection named "Kindle Tools") instead of first launching KUAL, pressing the entry "Cool Reader" there, thus starting Cool Reader's internal launcher. The same is true for KindCalc. This intermediate step is absolutely unnecessary for everyday's usage.

The last fw which allows using Kindlets is 5.8.11. That's what counts in my point of view.