Some put it on then get erect, some put it on after getting erect. Sounds to me like you bought some garbage clamps. Sad to say. If you can post pics of the ones you broke. If you get the ones that are in the constrictor guide, I don't think I've heard of them breaking, and I use them for heavy duty stuff not just Penis Enlargement, like actually clamping cables together with them....LOL....
Try to put it on both ways, and see which you prefer....that's the only advice I can give on the subject, it's all up to what you prefer. Holla