Astra Premium Sites are they the same as Astra Agency Sites ?
Astra Premium Sites is for Premium Demo imports.
They have free theme (Astra) and free plugin for demo imports, it comes with a couple of free demos (Astra Starter Site plugin).
Then they have paid plugin or Add-on plugin for unlocking more customization options. (Astra Pro)
Then finally, they have (Astra Premium Sites) which is more like the paid version of the Astra Starter Sites plugin. It unlocks more advanced demos.
Astra, Astra Starter Sites, Astra Pro and Astra Premium Sites are all different plugins; they add separate functionalities to the Astra theme.