The person who taught me Combat Sambo utilized a lot of attacks that targeted the weaknesses in the fingers, thumb, wrist, elbow, shoulder, neck chain. Most attacks were based on an opponent who is aggressively grabbing your clothing or forearm (or they are holding an item they don't want to let go of) this effectively controls the fingers and thumb leaving the wrist vulnerable. It works well against someone committed to their grip, but the simple defense is to just let go (limp hand). Wrist attacks are probably more effective and available in a gi setting. I have never executed a wrist lock that submitted someone in live resistant no gi rolling; however, I have been able to use them to disbalance/reposition to get an angle of attack, to distract them in order to do another attack or defend against theirs. I wouldn't rely on wrist locks for a finish but they do have an effective role. Just my humble white belt experience.