Rubber mats are all well and good, unless you really make chips... then they're more trouble than their worth.
I find them just fine around grinders, not so good around machines where you're throwing volumes of chips.
What I rather like is a wooden mat, built kind of like a scaled down pallet. Couple of 3/4" thick plywood crosspieces with open latice of salvage hardwood (old pallet lumber ripped) on top. Suspended wood has some give, chips fall through.
Cyclotronguy