I've watched it, and it's a very good spy movie. At the beginning, we see one of the communists spilling out details about the operation to avoid being shot, but our four protagonists don't know about it. The operation is kaput from the start, which makes sure the movie is always tense. All of the spies are smart, making moves to withhold/extract information from others. This feels exactly like what a spy movie should feel.
Unfortunately, I can't say I enjoyed the movie to it's fullest. There were moments where I couldn't absorb new information fast enough. All the characters wear the same clothes, which did not make things easier, plus I find remembering their names quite hard. A character/event flowchart would be a welcome companion while watching it.
From what I've been able to research, this is actually a prequel to the 2012 tv show "悬崖" (Cliff) by the same writer, Quan Yongxian. In an interview (https://inf.news/entertainment/bd5332246260958e06dc8ead644ec3da.html
), he said that in 2015 he had written the script for this prequel as a 60-episode show.
If this had been a tv show – or even a book –, where things could flow in a more friendly pace, this would've been a absolute must watch. Overall, it is a very good movie, and I recommend anyone interested to watch it, even though you'll scratch your head sometimes and may wish to rewind a bit to understand what is happening (though I didn't, and was still able to enjoy it very much).