How does the auto DJ compare to something like Pacemaker?

Are you referring to this? https://en.wikipedia.org/wiki/The_Pacemaker

I haven't tried that myself, but used the AutoDJ feature of Mixxx a couple of times. It's fairly basic, you have a playlist, setup how you want it to fade, and how fast, hit Play and off it goes matching the beatgrids and whatnot.

Yes, but they pivoted to a music app about 10 years ago. It worked great 99% of the time and had decent transitions. But they got bad startup incubator advice and ended up getting acquihired about two years ago.