I've tried it out, and it's much better than I expected it to be (I expected it to be about as buggy as Shadowplay and AMD GVR when they were first made public).
Unfortunately it's entirely useless for games running from a launcher (such as GTA V, Tomb Raider, etc.) because Action! still thinks that the launcher is the game, so it just records the launcher.
But that's not my main topic (there is always a way to get rid of the launcher). The thing I wonder is that, is it safe to shut the game off while Action! is saving the clip? The save time is really long, sometimes it lasts over a minute, so I don't want to lose the video if I quit early or the game crashes.
Will Action! still work in the background to save the video even after I shut the game down and return to Desktop?
Also, is it safe to record with the standard recording option? Like, if I'm sure that I want to record the entire clip and still want to keep a backup of the last couple of minutes just in case something happens?