The easiest method is to use a circular saw with a concrete cutting (carborundum) blade it will go thru it as easy as a regular wood blade cutting 1/8" Plywood. All the described methods work its just how much hassle you want to go thru. Use a circular saw/concrete blade one time and you will never go back to any other method.

Make sure you wear eye, ear and breathing protection.

Regards,
Bob