I agree, the Merciry 'fabric' kill cords dont last very long at all, I took the decision last year to stop using them and we use original yamaha killcords on all our outboards now.
You don't even have to change the end, as the loop of cord which secures the yamaha end fits nicely over the mercury killcord switch (although I always have to point that out to people new to our boats, as they always tell me I have the wrong killcords
)