Hello, If it doesn't say that the product is second-hand, it's because it's new. The Serein Elite is already a few years old, so the price drop is normal :)

Funny, I was looking for a Rode arm for my mic today. The plate at the bottom of the bracket can be unscrewed, yes. But I don't have anything to measure it with. According to Google, it's a 5/8" thread.

That's right, you can unscrew the plate and mount the bracket on a 5/8" (15.9mm) thread without an adapter.

This is not included and must be purchased separately. Would sell the microphone new and unopened for 180.