+1... tried both, MacID is vastly superior to Knock... I use MacID all the time. Knock was a gimmick that didn't even last a day.
Based on all the comments here I downloaded MacID. Have not tried knock. I actually had no idea that this existed, so thanks MR for the article. So far MacID seems straight forward and works. But having to take the phone out of my pocket makes it no easier really compared to typing in the password (except for the remembering part). But I can see how the watch could really make a difference here.
Will continue to play with it and see.