I can't see using a lanyard of more then a few inches on a top handle saw(ie: 200T) The very nature of movements you use while trimming would be greatly hampered if it had to stay attached to a long lanyard. Being clipped to your saddle makes it easy and less fatiguing, sense your grabbing for it non-stop and all day on some jobs. On rear handle saws I use a long enough lanyard i can cut either right or left handed effectively or pass it behind my back. On conifers I often keep my saw running while its hanging as I go up a few feet to the next set of branches(not so with a top handle saw on my hip).
I always stress to my groundman when sending up a big saw on a lanyard, not to send it up by the lanyard, so I can safely hook the lanyard to my belt before untying it from the rope. Dropping a saw on a groundie would mess his day up.
I have seen a few times in my life a big saw go over with the top, leaving only the handle hooked to the lanyard on the climbers belt, so a break a way lanyard could be a good thing, and I have a few times my self cut a big branch and have it rip my top handle trimming saw out of my hand, and though embarrassing, I am glad I wasn't using a lanyard. I have always made my lanyards out of 1/2in three strand rope, but if I was to buy one I think it would be one with the two rings so you could shorten it up some times if need. Beastmaster