This reversal is a great option for when your opponent is staying VERY tight and has his hand placed next to your hip so that recomposing Guard is not an option.
This is a very high percentage move, even against people who are larger than you, when done correctly. The most difficult part is the timing and needs a good bit of practice.
Other points of difficulty include pushing with your elbow and not the palm of your hand and making sure to get that far shoulder off the floor. Sometimes this can be difficult and requires some cardio as your opponent is going to be continually flattening you out.
The last point that you need to remember is to shrimp your hips towards your opponent. This is counter intuitive but absolutely necessary. If you are having problems understanding what I mean please watch the portion of the clip where I do this without my partner. Watch how my hips move and the pressure that i create with my elbow.
Thanks for watching!