Now that ClickHouse has released async writes you won't need to use the buffer engine anymore, which has been always a non recommended solution anyway.
Maybe, are you already using that feature in production? Buffers are available for years and just work. Hard to say how async inserts perform in real applications.
I also use buffer engine, don't get me wrong.
The only reason why I'm not using async writes is because I only run Altinity certified versions in my clusters do I'm waiting for it.