Hi there,
I've just bought the chained fields plugin. I've installed it on a fresh joomla 3.3 installation with K2 v.2.6.8 (+ french language pack) and JA K2 Filters. Nothing else (no template or component from third party devs)
I've the same problem, I've followed the steps from your video with just 1 parent field (4 choices) et 1 child field (up to 15 choices to dispatch on the 4 parents choices).
Everything was fine but, when I go to the element creator from K2, the chain doesn't work.
You could take a look if you want, send me a email to webmaster[at]ffpp.net, i'll give you full access.
Thank your for your help !