The story is that it's used in production and works quite well (but I am pretty biased as I developed most of it). If you want some examples take a look at my book[1] which includes a whole chapter where you build a chat app using Nim's async/await. The code for this is freely available[2].
1 - https://book.picheta.me/
2 - https://github.com/dom96/nim-in-action-code