I own one of these mowers and like rvsuper said, it is reverse assist. You must pull backwards on the unit to get it to move. In my opinion, it's of little to no use. God help you if you get it trapped in a tight area nose down on a slope. Call a tow truck.
I have an Exmark Metro HP 36. On belt drives it is REVERSE ASSIST, which basically means DON'T EVEN BOTHER kicking the gear shifter to "R", just use the gripper to put it in NEUTRAL and then pull it back. You get real good at using any sort of slope to help you back it up. Takes some planning, but after awhile you do it without even thinking. HYDRO full power reverse is SWEET but not worth the extra $ FOR MY SITUATION.