Contract Beasts are constrained by time, but Exchange Beasts are different. They are solely controlled by Alchemists (after all, they cannot be considered Living Entities, simply fabricated imitations). As long as the Alchemy Equation allows, Exchange Beasts can be "summoned" without restriction. However, controlling the Exchange Beast after summoning and making it part of oneself is what distinguishes the abilities of Alchemists.
Like most professions, the strength of one's Spirit Power determines an Alchemist's capability. Those with powerful Spirit Power can imbue their manufactured Exchange Beasts with their own Spirit Power, making them their eyes, their ears, and ultimately, their doubles.
For Alchemists with weak Spirit Power, however, the Exchange Beasts they create can only serve as decorations. Dead Objects lacking Spirit Power are merely ornaments.
