Welcome. With all due respect, did you use the search?
First gen t36 receivers often need a readily available cam pin if using German parts kits. Gen2 are good to go. If receiver is marked 'choate', its gen1.
That being said, tommybuilt @tbostic stands behind his work. Buy with confidence.
The GSG9 parts being used are overall very good. My complaint would be they seem more prone to rust. Bolts and lower internals especially, in my experience