I think the different schools that have separated from Grand Master Yoo Soo-Nam are diluting the technique of Sipalki Yeon Bi Ryu, as can be seen in these hyons performed by members of Sipalki Mubikwan:
http://www.youtube.com/watch?v=tCm6AFwzgIM
http://www.youtube.com/watch?v=CWx3zwzvuD8
http://www.youtube.com/watch?v=71CExGapru8
http://www.youtube.com/watch?v=g7XUAHVlXow
http://www.youtube.com/watch?v=Wwq2RLsZJZU
Swallow