While the king pin stabilizers look like they might do a good job, and we've never heard anything to the contrary, we don't use one. Our RV's 6 point hydraulics keep the rig pretty stable. For us, the added stabilization they might create is outweighed (pun intended) by the need to stow and carry them around.
That said, many people do swear by them. We recommend trying one out if you're having issues with the option to return the product if it doesn't help.