Pontius,
With reference to your last comment, I think you are refering back to MNPS, when you needed 2 independent long range nav aids to go above FL270 in the North Atlantic. Omega was one system that met the requirement, hence presumably the fit to Nimrod.
Still, a properly fitted, funded, system has to be better than a hand held GPS, intended for use by foot soldiers, attached to a wall with wiring up to an aerial installed in an old sextant mount!