As others stated, they are not chocks to prevent the trailer from rolling, but are designed to prevent rocking between the tires which is what causes the movement in the trailer when walking around. You should always use regular wheel chocks(not chalk, the trailer will grind them to dust) when you park it, let the tires cool, reset the chocks, and then insert the X-Chocks, after you have the stabilizers down and locked. One of the things stated several times in the paperwork is once installed, do not move any of the stabilizers or front jack or the X-chocks will get damaged, or cause tire damage.
I have both regular wheel chocks, the plastic ones from Walmart, and X-Chocks and used them both this weekend for the first time, and they do help keep the trailer stable, but the do need to be setup correctly.