I would think the Magic Mats are better. They are made of silicone, while the frog mats are Teflon coated fiberglass. BBQ Guru use to make a silicon mat to prevent food from sticking. I bought some to use on my grill. They work great in preventing food from sticking. I would expect the Bradley mats to perform just as well.
You should still spray your racks with a nonstick spray, before laying the mats on the racks.