This is the MXR Micro Chorus.
The short story is that I love this chorus. It creates a lush, velvety warmness to my tone that works wonderfully with fretted and fretless bass. First outing was at Carols in the Park, where Silent Night (and other classics) were supported by sweet, chorus-y plushness that filled out the mix nicely.
The controls are dead easy. The switch turns it on. Groundbreaking, I know. Turn the knob to the left for more subtlety, or all the way to the right for inspired wonkiness. So far, my go-to tone is somewhere between 10 and 11 o’clock.
This one is definitely a keeper.