I have one, its worked wonders on me.
Basically, make a circuit of 4-6 core exercises. You go through the circuit non stop, then rest once you finished. Do it 3 or 4 times. Heres an example:
Weighted V-ups, 12
Chinnies, burn out
Plank, 60 sec
Weighted Russian Twists, 20
Weighted Side Extensions, 10
Side Plank, 60 sec
----Repeat 3 to 4 times. Rest for one minute. No rest until you completed the last side plank.