It can be used for any digital Input or Output. To connect a switch to it all you do is connect one side of the switch to ground and the other to the pin you choose, go into Ports and pins and for instance choose the Jog X++ in the Inputs and set it up for Port 10 Pin (whatever you have connected)
Anything like a MPG that is timing critical can NOT be connected to it at this point in time, I think its response is 100ms. There may be Encoder Inputs soon but dont think they have been added to the firmware (or however its done

) yet.
To Install all you do is download the software and start it up with the PoKeys connected, it will then say it needs to update the firmware, it will do this (internet connection needed) You then need to set any pins you want to use as outputs in this software and then it will write it to the device. Inputs dont have to be asigned. You also need to install the plugin and enable it, then when you go to Mach you can look at the plugin and watch the I/O change as you press keys or whatever.
It can also be set up as a keyboard emulator so that a button press will do a keystroke or combination of keystrokes.
Not sure on the probing, that might be timing critical?
Hood