Also, it seems to be hard coded to run on Maya 2017 only: https://github.com/Swannotron/RoadkillProfessional/blob/master/MEL_script/RoadkillProInit.mel#L666
In 2018.1 there's an explicit Model Assist mode to bring back this behavior when no SGs are assigned, but I don't think it's in the latest 2017 update.