I got this thing running finally.
The documentation was a little poor but after a couple rounds of correspondence with the supplier in China I think I have everything in order.
On thing I really like about it is that it has a little spindle relay.
It appears to be 5A, 120V so that could work with a Dremel.
An ohm meter placed across terminals 1 and 3 on the right seems to vary between infinity and 0 when I click the spindle control in Mach 3 so that’s promising.