Don't use them. We have installed leg leveler' on all our ladders many years ago. Too many accidents can occur when using independent wedges etc. for ladder supports. Leg levelers never shift once they are set into position by the operator.
X100!
I know many operators that use them and like them, but we threw ours away. Way too dangerous and they like to flip. It cost my workers comp insurance $12K for plates and screws to repair a broken foot of a employee last season. Not to mention a increase in premiums as they will eventually get it back. All better now and he is back to work, but it cost the company $50K-$60K with an additional lost in gross wages towards the end of season, as he was out of commission.