Has anyone built this Fluxgate Magnetometer (or variation thereof)

I'm trying to build a device to measure the Earths magnetic field in the nano Tesla range. Massive coils and instrumentation amplifiers are the traditional way but I came across this site where the author built one in 1992.
https://www.bealecorner.org/best/measure/fluxgate/
Looks simple enough but I've no experience in fluxgate designs.
Opinions?
**broken link removed**

Hi Bill,

those sensors are to be found preferrably at airports. They are built in the wing tips of every airliner.

Removing one them won't be recognized quickly. There are several for backup.