The hardest part about this exercise is sitting on the floor with your legs extended out. Those of us who have tight hamstrings, will struggle to be able to do one or all of 3 things:

1- Keep the legs straight

2- Keep the back straight

3- Keep the pelvis from tipping under.

So them easy solution is to use a pillow under the hips to help you.

(And then try to sit on the floor daily to improve)

The sliding of the hands forward stretches the spine. Holding the 3rd one gives the body a chance to hold the stretch and breathe.