When is it worth it? I probably fray an iPhone cord once every few months. That’s it! That alone should make you just buy it on Amazon whenever your fray your cord. The cost of buying the glue is cheaper than the cord.
If you stick it in your draw and can use it for other projects, that’s a bonus. Will I find it in the drawer? No. But I’ll probably just fray my cord again and order this and save the difference!