Yoko-tomoe-nage is the dominant form of tomoe-nage in competition judo today. It is harder to learn than traditional tomoe-nage because you have to rotate your body as you enter into the technique. With traditional tomoe, you fall straight back, which is easier for most people to do. But the yoko-tomoe is more effective. So, it's worth learning if you wish to incorporate tomoe into your repertoire.