I think anything you attach to the saw is too Rube Goldberg.
If bucking a long log, I have a loggers tape measure and attach the hook to one end of the log, then, with the tape attached to my belt, walk to the other end of the log streaming the tape out behind me. I will either use a hatchet to make a mark on the log every 16", or use a scrench (screwdriver-wrench tool for chainsaws) to scratch a mark every 16". Easy and quick, and then I walk back down the log in the other direction with my saw making cuts, reeling the tape back in.
If I am working on shorter logs or don't want to use the tape measure, I have a 16" stick of wood that I painted the ends with bright green marking paint (what I had around at the time) to make it very visible. I will use that to pace out 16" chunks and mark the log with hatchet or scrench.
For firewood you don't have to be perfect -- shoot for 16" and eyeball it. When cutting saw logs, I am a little more careful.
Sure make me look that guy up, then I see you on this youtube video promoting this Dr. Seuss measuring attachment for chainsaws, I did want to give that a look-see but couldn't find it for sale, maybe it had tomany issues, the only issue I seen I saw was, he should've thrown that Shtil away and got Husqvarna 550xp>>> The Chainsaws Rule, Cuts Firewood The Same Size Every - YouTube