I just bought the same exact one on amazon. They work well. I've been using them on clients for years. They give you a general idea of someone's body fat. I find that they tend to be within 3% of what a pinch test would show. Pinch tests are more accurate in healthy to low body fat individuals but this hand held device would be more accurate in a overweight to obese individual because it could be hard to impossible to get to the muscle on a pinch test.