Do you know how good SML's concurrency story is these days? I tried http://mlton.org/ConcurrentML http://mlton.org/ConcurrentML but gave up due to lack of time

Do you know how good SML's concurrency story is these days? I tried http://mlton.org/ConcurrentML http://mlton.org/ConcurrentML but gave up due to lack of time and the state of the documentation.