Rather, bad for your back.
Saw this Justin Rose tweet. My back hurts looking at it but I guess it's sort of like that back machine workout where you're on your stomach hands behind head and you raise your back.
Is this kettle exercise good for your back?
TheSandTrap.com Top Picks
That i believe is commonly known as a 'kettle bell swing' and works the entire core and posterior chain in the way he is doing it (so abs and lumbar erectors, hamstrings and glutes). His form is good, notice he maintains his proper lower back curvature throughout the motion and keeps his neck in a neutral alignment plus a good degree of thoracic extension. He is doing the exercises safely.