The hook and wire ties have no sharp edges that will scratch the paint. The hook is rigid and sufficiently open (which allows me to set it at different places, depending on the load arnacher).
The tensioner has good elasticity and sufficient strength in most cases (if not I use straps).
Having a different color per length is also a very good idea that helps to identify the right tension to use.
I recommend this product which is much more convenient (and less ugly, too) than conventional tensioners.