I dig the kneebar the most I can only do it on upper belts and not on fellow white belts. I have only been able to get a kneebar on a blue belt, but we spoke before we rolled and agreed we could do them between the both of us ( im a white belt ). Otherwise the school I go to, kind of frowns upon any type of leg and footlock.

I hear if one is locked on you ( a footlock ), at first it's like "okay..." but then the next day it can really hurt and sometimes it can last for months... impeding your progress as a consequence.