As Stu says,
If you are already a GGTS owner, there is a specific AVS for you with the extra parts you'll need for it to work on your model GGTS.
If you don't currently have a GGTS, then you will need to purchase the combined unit.
The AVS will only work on one or other of the GGTS units, old or new.
If you want an autofeeding system that will work on any mod, I'm afraid you'll have to wait until that version is back in stock - I don't know when that will be.