It's an exotic among exotic poses. So fills u with exhilaration. .even a master like BKS is not above that thrill as mentioned in his Light on Yoga book. This a very tough variation of the basic one. In the latter the top leg is held with this leg lock. Holding the bottom leg requires tremendous control over balance.
Tip: Master the basic. Then use a wall to lean while experimenting with this version. It falls in place, suddenly. Pure serendipity. .