I have one field fenced with braced T-posts at the corners. Pinlock insultators broke under the wire tension, but these are a permanent fix. I also use them at the corners of my rotational paddocks, where they eliminate friction as I draw the wire around, saving wear and tear and making setup/takedown easy.
Pros: The best product for fence corners.
Cons: Steel threads are soft. Do not overtighten; and they don't like to be removed/reinstalled.