This overhead press variation forces you to have perfect form. It will immediately expose lack of t-spine extension or exaggerated extension through the lumbar region by making you lose your balance. Overhead presses are difficult enough as is, but throw in a kneeling component and you just raised the difficulty bar several notches.
If you're capable, kneel on a bench rather than the floor. The fact that your feet can't anchor into the ground for support increases the difficulty.
To complete this move successfully, every facet of form and technique must be dialed in. Because there's little room for error, grab a spotter the first few times to make sure you don't face plant.