Hi,
if this is the one i got (looks pretty much the same) it is nothing more than a usb keyboard that only sends one letter on pedal down. mine had a special app attached that would let you change that letter to your own need, but that app only worked on windows. so you might be stuck with the default letter (usually "a", "b" or "c")
still, since this is basically just a one letter keyboard, it definitely works on OSX and you don't even need [hid] but the [key] object. be aware though of repetitive sendings when pressing the pedal too long, you might want to filter those out.
also, my pedal is cheaply built, not what you would call rock-solid. but it does the job alright (well, the concept is simple enough) and it's cheap.
best
oliver