SQ-1 vs Beatstep Pro ?

They are different beasts. The Korg SQ-1 is more powerful than the SEQ16 because it has MIDI out, CV/Gate out, different running modes (up, down, pingpong, random, etc), has a quantizer (Major, Minor, off) and can send either one 16 step sequence or two 8 step sequences in parallel. It plays really well with MIDI gear, Eurorack and also the AE Modular. While it can sequence the Volcas (via MIDI) I'm not sure why you would want to do that, as all the Volcas have their own sequencer built in.

The SEQ16 only runs in one direction and has no quantizer, but it has a ratchet feature (repeat a step multiple times), is smaller, cheaper and better integrated into the AE system.

While I still have the SEQ16 and use it very often within my AE patches, I sold the SQ-1 because I was looking for a more complete sequencing solution outside the AE.

The Keystep is also a very capable sequencer AND arpeggiator and I've use the latter very often in my videos.