The one from Jegs has a thin PVC outer shell. It really does a great job keeping water out, but rips on the corners easily. It breaths through the seams. All the fabric ones turned to dust in about six months on me.
I have to wonder about the breathing through the seams bit. So are the seams supposedly the only areas that aren't made with the PVC outer shell? The seam areas don't seem like enough area to allow the main portions of any cover to breathe out any trapped water/condensation. And some condensation always gets under the main body of any cover especially if you get some rains and then hot days mixed in.