I like the fader for automation, I use it a lot, together with the transport controls, custom controls and track controls. The EQ section is a bit useless because the knob mapping is upside down and the acceleration is a bit too extreme to comfortably work with them. They’re ok for quickly accessing send levels, although the acceleration thing still holds.
The AI knob is indeed stepped.
Seeing as you already have most of the useful functionality of the CC121 covered with your CMC’s, I don’t think the CC121 is worth its asking price for just a motorized fader.