Most of the "sand vests" you mentioned are made of canvas and filled with sand. There is not much difference between a standard vest and an ordinary vest. As long as the load is within your tolerance, you won't get hurt. It's just a load, depending on what kind of exercise you do with it. If you just run with a load, then a "sand vest" can be used for a long time, from 65438 to 00 or 8 years.