In my industry you get to wear a harness alot. After seeing a hanfull of videos and doing classes on harnesses I would recommend you use the harness and not the safety belt. The amount of force that is generated in a fall is a lot.
we have actually started to get away from the stretchy lanyards and going to the retractable lanyards. They are more bulky but will only allow you to drop a inch or so instead of a few feet.