This is one of my favorite Foundation Training exercises! It is very strengthening for the back and the glutes, and when you add the decompression breathing, you can feel the length and the strength in your back. Getting good at this position also can help you with kneeling work like gardening, playing with kids or pets and then cleaning up after kids and pets.
If you are going to try this, be sure to have some extra padding under your knees, you can roll your mat toward you and double it up or place a towel under your knees.
The key is lifting the back long with decompression breaths and then hip hinging back while you lift the torso and be sure to keep very little weight in your feet, it will feel like you could fall forward but hold that position! The reason this exercise is so strengthening is because your muslces that support the back of the body are working very hard to prevent you from falling forward, a very "functional' way to strengthen your back and glutes without compression.