Just sharing my experience with both helicoil and threadsert. My 80 KZ1000 had a stripped spark plug hole. I changed plugs often and regularly. The helicoil installed by the previous owner didn't last more than three plug changes. I had a professional install the threadsert and problems were solved. Numerous plug changes and still tight as when first installed. To me, really the difference between rookie and pro.

Regards.