Great comments and suggestions! Thanks much to all who replied.

My thought when I proposed the question was:
- The lockable straps replace the straps that usually come with the roof rack. Attaching them involves no more time, effort, or equipment than normally attaching the kayak to the roof rack. I can lock them when that seems appropriate or just cinch them normally when locking is not needed.

Following are certainly not criticisms, but reactions to some of your suggestions:
- A stainless steel loop/ring would add (admittedly negligible) weight to the kayak, and who among us wants to add weight. There is the weight of the loop and fastener, as well as the epoxy in the drill/fill/drill attachment hole.
- A cable that is attached only when the car and kayak are left unattended is something I could potentially forget (Why did I come into this room? (Folks near my age will understand that.))

Thanks again. This is a great group of very helpful people!