"A grab-bag of all sorts of Fading Suns setting material for d20 games, including alien races, prestige classes, occult powers, cybernetics and the mutated Changed."
However I believe Heretics and Outsiders has d20 stats including the rules for demon summoner bad guys.
Also a bestiary again with d20 stats is due shortly.
Besides all the dual stat stuff, my hope for the Companion is that it will fill out those bit in the d20 rule book that were in the main Fading Suns book. Together I hope the d20 FS and d20 FS Companion provide a very comprehensive core FS game.
Because they weren't going to produce it at all. They were just going to rely on people picking up the dual stated supplements. However many fans begged for it and so they went with it.
Also though Holistic Design produces many books I think their production schedule is full with their more profitable main lines so they the d20 FS Companion in 2003.