I have never used the plastic yellow chocks.
I bought the X chocks right away and that is all I've ever used.
Although I did see some black rubber caulks like the yellow plastic ones at a store the other day....but they were $25 each and quite heavy.
I like my X chocks between the tires as they give a positive lock and never slip!
Made by Camco.....
Place between your tandem tires to prevent both forward and backward movement while parked or rehitching. Wheel Stop installs easily between tires, stabilizing your trailer with one piece of equipment. Designed to fit 26" to 30" diameter tires with tire spacing of 1-1/2" to 3-1/2".