Imperial Devices is the quest associated with The Thousand Maws of Toto-Rak. You can only have one of the three Imperial Devices quests active at a time (you can't complete all three at once), but once you complete it for say, Gridania, you can go to the Hall of Flames or Maelstrom Command and accept the other versions of it. The same goes for Into The Dark, the quest for the R45 dungeon.

You can't get locked into any of the Grand Companies permanently until additional missions are added in 1.19.