When considering wire tie strength, there are two very different ways to measure how strong it is. This requires that you factor in your actual application for using the ties.
Tensile strength measures the amount of force that the tie will resist before breaking. How much force is required to break it into two pieces.
Mechanical strength addresses how much practical force is necessary to force the tie’s locking mechanism to fail. This considers what is being bundled in the tie and how tightly that tie needs to be pulled as it is latched.
Not all ties use the same latching mechanism, so similar looking wire ties will have varying mechanical strengths.