What are the Ultimate Tier relick Items all about?

It seems each relicker has an absurdly expensive item (3200 scrap)

Rumourmaster’s Network and Breath of the Void are the ones that come to mind, im sure there are others too

What do they actually do?

The Rumourmaster’s Network doesn’t have any uses at the moment, but the other three had or have a use. Breath of the Void and Veils-Velvet had a use in a SMEN specific location. There’s no telling if that use will come back with the content, however. The Reported Location of a One-Time Prince of Hell can be used to upgrade your Brass Embassy Guest Room into a Sanctum.

fill up your collection, so you can get as close as plausible to achieving one-of-each.