The one in the photo looks like a "Tamper Evident Seal" available from
http://www.tamperseal.com/luggage-seals-c-25.html

I break a nail every once in awhile, too. I find that using a metal nail file to open the ring helps. For me, the thing is threading it through those zippers that go together and have the hole to put the ties/locks in. Usually I'll give up and just put it through the top holes in the zippers.

Do you think it would work better if I left a ring on each zipper pull and just linked the rings together?

Chollie - if that's a checked bag I wonder if it would just give the bag an easier way to get caught on something, especially on the conveyor belt.

I use cable ties, but not really for security, but just to keep the zipper on the bag from opening, and for express flights where I have to give up my carry-on. I have had my TSA-approved locks opened (the little red flag is up) without any letter from TSA inside; OTOH, I have had the letter when they cut off the TSA lock (why ?) and didn't replace it with anything.

Zip ties are 'not approved' items, LOL.
YYZ-LGA through Nexus line.
Security found my safety razor blades (shoulda left them at the office) and in the same clear bag were a few 5" zip ties. She grabbed the bag to go talk to another sec agent and they both decided they were 'not approved'.
Chuckled and commented that it was hard to keep up with what was a 'security risk'. She laughed also and kept on going.