We always use zip ties (nylon wire ties) and never had a problem. They are cheap and if they cut them off it is no big deal. We always pack a small pair of scissor in our carry on, to cut them off.
We've used zip ties for years, even before the current security guidelines say you could not lock your luggage.
One thing to keep in mind is that the lock doesn't really keep anything safe - it just keeps the suitcase zipper shut. There are lots of keys out there so anyone who really wants to unlock it, can and you would never know. At least with the zip ties, there are many different colors/styles, so if someone cuts and replaces it, we would know.
I would also not be so quick to say that all missing locks are due to TSA cutting them off because of laziness.
I traveled with a friend who used the TSA approved locks and she wanted to make sure she was there if they checked her bag. As her bag came out of the little conveyor belt for the xray machine, it hit just right and the lock popped right off. She thought the TSA person had just not relocked it, but he showed her it was popped open and broken. He said that happened quite often - if the bag happens to hit where most weight hits on the lock, it will pop. There were a bunch of broken locks on the floor just where we saw her lock fall, so there was quite a bit of evidence of it happening. He put a zip tie on for her to hold the zipper shut. He said if the suitcase was locked and the lock breaks, they are supposed to replace it with zip ties, but most of the time they don't notice which locks came off during the xray.
And, if the locks get hit in that same way anywhere along the process of baggage handling, the same thing can happen.