mb9

My grandson was born with an abnormally developed "X" gene. I believe he inherited the condition from his father who seems to enjoy anything a reasonable person would run from. In the interest of safety and my blood pressure, I'm looking for DC motor speed controller. Specifically, I need to limit the output of a 24 volt motor on a razor pocket bike. I was looking at this kit, http://electronickits.com/kit/complete/motor/ck1400.htm but I'm not sure it will work. Will this do the job ? Does it need a separate power supply? HELP!!