Honestly not all that much to report here, it's the origin story of the Cult of Skaro, pre-time war. We get to see Sec's victory over the mechanoids that shows why he's chosen to become Sec, we hear The Emperor's reasoning for creating the cult, him giving them each names, generally just some fun stuff there.

Also learning that Sec's casing is a reinforced but expensive version of dalekanium answers some questions as to why he looks like that (though admittedly also brings up a lot more generally about why no other daleks do).

I've also realized this is the last story with The Cult of Skaro I hadn't seen, and their only appearance outside the TV show which surprises me, I know The Emperor has been touched on in other media but not The Cult?

I guess there being a straight line from The Doctor finding out about them through all their appearances until they all die is probably why, but still, absolutely *nothing* more done with them surprises me