This is the latest release from Motorsport NZ regarding the use of Frontal Head restraints with regard to regulation requirements and installation

Clearly there are many considerations with regard to the use of a FHR which must be all taken into consideration to have a correctly installed device befitting to the type of seat and harness which is fitted to the car being used.
It now appears that a 4 point harness cannot be used with a FHR, only 5 or 6 point harnesses.

Name: MSNZ FHR1.JPG Views: 604 Size: 90.1 KB

Also below are the FIA installation guides which have been provided by MSNZ:

https://www.fia.com/sites/default/fi...tion_specs.pdf

https://www.fia.com/sites/default/fi...ation_spec.pdf