Yes mu-metal is quite efficient to shield low frequency and static magnetic field. But 800000 is a great factor and it would be difficult to measure earth's magnetic field with that much shielding. You would not be able to verify this claim. You can look at the attached information.

It is known that several layers are very efficient to shield the magnetic field. Sometimes the outer shield can me made of ordinary steel which cuts down the stronger high field. We sometimes do neutron spin echo measurements in mu metal chamber. The cost is much lower than superconducting shields that need cryogenics.

Have a look:

http://www.magnetic-shield.com/faqs-all-about-shielding.html

Also read the book:

Jiles, David (1998). Introduction to Magnetism and Magnetic Materials. CRC Press. p. 354.

Thanks Tapan. I know this company. As seen there is huge difference between 1500 and 800000. This is really suspicious. Have you ever used such zero gauss chambers before?

We use mu-metal chambers for doing polarized neutron scattering experiments. These are however fabricated at our Institute. We do not buy from these companies.