CPU usage was definitely noticeable, but not more than 8-10% IIRC (on M1). I remember lots of tiny 0->10% spikes rather than a steady ~5% when viewing the CPU graphs.

it says on m1 and m2 macs it uses 20-40% of one core, or up to 5% of all CPU. Local transcription is expensive (in my experience).

It appears i am misremembering, because i thought it was for windows. Oh well.