I have a VistaCNC pendant also. Wouldn't be without one once I tried it. The model you get may depend on the driver software you use. For Mach 3 I think any will work. For UCCNC and others not so. I started with a M1 and upgraded to a P2-S for that reason. Just a little info to consider for those interested in these.
As a side note get the optional longer coiled cord and the magnetic backing. Both are convenient.