That one looks identical to one that I fitted to my mill about a week ago. I was going to make one using an Arduino clone but then I saw ready made ones on the net. It must be the best bargain on the net, I think that it was about $5 with free postage. I got one to try but now I'll order more and fit one to everything in my workshop that rotates.
Hi Tony, Beware of some of these that don't have a wiring diagram can be a problem. I bought the magnets that have a hole drilled in them to mount on the pulley by tapping the pulley and screwing them on there along with a counter weight.