  In this last of a series of three papers on the development of an advanced
solid-state neutron polarizer, we present the final construction of the
polarizer and the results of its commissioning. The polarizer uses
spin-selective reflection of neutrons by interfaces coated with polarizing
super-mirrors. The polarizer is built entirely in-house for the PF1B cold
neutron beam facility at the Institut Max von Laue - Paul Langevin (ILL). It
has been installed in the PF1B casemate and tested at real conditions. The
average transmission for the "good" spin component is measured to be >30 %. The
polarization averaged over the capture spectrum reaches a record value of Pn ~
0.997 for the full angular divergence in the neutron beam, delivered by the
H113 neutron guide, and the full wavelength band lambda of 0.3-2.0 nm. This
unprecedented performance is due to a series of innovations in the design and
fabrication in the following domains: choice of the substrate material,
super-mirror and anti-reflecting multilayer coatings, magnetizing field,
assembling process. The polarizer is used for user experiments at PF1B since
the last reactor cycle in 2020.
