Eiffel Tower Vases-Disaster waiting to happen or not?

So I have researched the Eiffel Tower Vases. Yes, they are just fabulous. I have found a site to purchase them and they are fairly inexpensive. I have also found the foam to make the bouquets bigger. BUT. Here is my question: Has anyone had experience with them at thier reception? I have actually found them in stores and they feel so...tipsy! Will they fall over if a guest ::bumps:: into the table? I've read that some people put river rocks inside them to give them more stability. Are Eiffel Tower Vases a disaster? I am opting to use smaller, low centerpieces for half of my tables and could easily forego the tower vases if they *might* cause a problem. Any thoughts?