The movement is quite simple in my opinion and it has many instances where it carries over to bigger compounds. It is a great overall strength exercise however if you increase the number of repetitions and you spend more time u der tension in each position, quickly it will become a tough conditioning piece as well.
The first phase of the movement is where most of us will find the challenge, including myself ;) Most people put too much emphasis on the loaded arm but not the base arm. This is where they perform a sit-up, crunching the spine and trying to compensate for lack of stability. Instead, think of driving the elbow hard to the ground to activate obliques and push the heel of the bent leg hard into the ground to activate the gluteus.
Think of it more as a rolling exercise, not a sit up.
…you will thank me later :)