We call it Yondan in AJJ and as a kyu grade I don't have much experience, but I am aware of the gakun grips used and I have had one lesson in the kata. I have found that I naturally want to apply yondan techniques in my knife defence. My sensei knows of my tendancy to apply yondan gakuns in knife defence and has given me some advice, which has been very useful to me but I know it will take years of practice to be able to apply them effectively everytime. I am beginning to see the progression in the different katas we learn from Shodan to Nidan and Sandan to Yondan. I am beginning to make the connections in my mind and body of the power of smaller techniques such as yondan for leverage and compliancy.