I have looked at them, however I don't like the fact that there is no indexing mark built into the system.

What happens if you happen to bump the fletch on your arrow after it is nocked? With this system the arrow will turn and potentially screw up your arrow flight as it bounces off the rest or whatever.

No thanks. If you are looking for a better nock then consider using Beiter nocks. They are probably about the same cost per arrow as the NAP thunder balls, don't require any extra weight added to the string and are as consistent a nock as you can buy.