The other warning on X-Chocks was not to operate the jacks while they are installed. I can't find that warning now but if you follow the steps of installing them you see that you remove them prior to using any jacks to hook up your RV and you don't install them till you have the RV level. Here is the steps to install X-Chocks.
Also the X-Chocks says check them daily and here is the quote from the step instructions: Step 6: Each day re-check jack screws for tightness as jacks may settle into soft surfaces and become less stable. Tighten jack screws as needed.
http://norcoind.com/bal/howto.shtml