They essentially work the same as a polarstar, though you install them in your existing gearbox instead of replacing the whole thing. The advantages of this are the SMP will fit a wider variety of gearboxes and AEG bodies and cost less than a full unit (and for some reason they are more gas efficient). Polarstar has already released their own competitor to the SMP, the Polarstar JACK. I haven't seen one around springfield yet, but all of the fields I have played at the past few months have been filled with them.