Hi,
They work. Even with the latest
K4PC 1.7.X. You just need to use the very very latest versions of the
DRM tools (today that is tools_v4.7) and if you use the calibre plugins from tools_v4.7, make sure you have removed all earlier versions of the plugins.
If you run into problems when using the very very latest tools, then let the people at ApprenticeAlf know so they can fix things if need be.