We have used nothing but Heli-Coil Brand thread repair tooling here for well over 2 decades.
Thousands of dollars tied up in that tooling here, in both metric, and SAE.
When installed CORRECTLY, they are a very postive repair.
Note on this, is that we've found to maintain that insert is in the hole about 1 thread below flush, on both sides, and naturally the tang is removed in a very swift action, not to create a potential problem with the last thread.
While doing contract machine work for McDonnell-Douglas, in St. Louis, Mo., many years ago, their drawings stated Mil-Spec part # such and such, Heli-Coil insert, to be installed at the original point of manufacture.
Must have been a good reason for that?
Another VERY GOOD thread repair, that we very recently used on the case studs of a 124" blower-equipped bike,(upon client request) is Lock-N-Stitch Permanent Thread Repair.
These are designed so that the more pressure the fastener recieves, the more it bites into the parent material.
Once locked in place, they are also pinned.
Mighty tough set-up.