Pretty much RzeroB, difference is when it's on the front brake it's either on or off cause your holding it locked on with the button, blocking the rear allows brake control so if you want to creep forward you just ease off the brakes a little and re apply to stop forward motion, while not heating your rear drums up, just a matter of how you plumb it in. I'd have to check but maybe if you mash on the brakes and then press the button it "might" lock the rears until the button is realeased, not sure on that