A lot like that, except when we do it, you'll land on top of the box before hopping down. Don't try to sideways jump over the 20" box!
Also, we love that people are getting more adventurous and trying out GHD sit-ups. But doing them correctly means understanding them. In the GHD sit-up, your abs are not the movers of the trunk; the abs act to stabilize the midline ONLY (that is, keep the spine neutral). Here's Greg Glassman explaining the details:
My two cents': the full range of motion thing can be taken too far. Don't try to reach for the ground (especially on our GHR, which is pretty tall). Only go back to the point your knees, hips, and shoulders are in a straight line. Do NOT hyperextend the back.