A Load Distribution Problem
The idea behind the unlevel edge is to distribute more load to the index and pinky fingers when training the finger flexors.
The design is intended to both increase strength and capacity while reducing injuries.
Disproportionately, when climbers only use a flat edge with a fixed depth, the middle two fingers take most of the stress.
Indeed, this doesn't mean that flat edges are dangerous, but they undoubtedly accentuate this asymmetry, especially when adding an external load.
In the illustration, the blue lines depict the ray length, the distance from the scaphoid tubercle to the end of the first finger bone in each finger.
For climbers who often face PIP joint injuries in the middle two fingers, using a more ergonomic edge is a practical solution.
It's a way to get in your training and reduce the stress you can't avoid while climbing.
The most common times I suggest using the unlevel edge are as follows:
Persistent PIP joint injuries of the middle two fingers
Peak force strength training in the half-crimp (lifting, curling)
Off-the-wall capacity training with the @tindequipment
Warming up the fingers (curling, lifting, pulling hard) before climbing
The recruitment and capacity gains with our training (muscular) will transfer to our sport as long as we are doing our sport more than our training.
Most athletes do enough flat-edge training on the climbing wall (coordination, positional stiffness, power) to justify doing less of it with our training off the wall.