-Anytime you use a grip like this (like doing pullups on hanging ropes, or hanging a towel from a pullup bar) you are at an extreme mechanical disadvantage, and it requires incredible grip, wrist, and forearm strength (in addition to arm, shoulder, back, and core strength). So, I consider these the most challenging grip progression (currently) offered at Atomik (outside of thicker versions of these, obviously).
-If you are a beginner or strapped for cash, don't bother buying these right now. Buy the regular pegs and thicker versions of them, as well as the ball pegs. Then when you get strong enough, come back and pick these up...and feel like a beginner all over again (and smile because you love the challenge!)
-As other reviewers have stated, these act like lever-arms, and the lower you grab them, the more they are going to want to come out of the receiver. Grabbing them higher will help to mitigate this, and grabbing them so that the peg comes between the index and middle fingers produces the least "pull-out force", as long as it is comfortable to do so (bigger hands will find it easier).