David, I use the same technique on all synthetic twine or rope except I use a damp rag, it seems to cool the melted material and shape it at the same time.
I also (when I have time) whip finish the shoe lace ends. I usually use embroidery thread ( I think that is what I had around the first time I did it, so it stuck).
You can see in the pictures below, I now try and match the shoe lace. The older red/green is on my old leather hiking boots, I did that one back in 1980, so yes I think whipping lasts pretty well.