Just does not work
The picatinnny rail installation is very poor in quality. Main screw is too soft. The idea of the adjustment in order to get the indicator levelled does not work at all. I fought 2 hours getting this indicator level in place and when finally attached so that it would be securely in place, the screw has lost its inner edges. When opening and closing the system, I have to carry additional small reliable pocket level and check before shooting whether the indicator is still reliable and it needs constant little twisting and adjustin with your hand. The same system will most propably work with barrel attachement and getting the level calibrated will work in that kind of system. I really wanted this to work because picatinny mounting is so handy but I cannot continue shooting with this but detach the indicator with pliers due to broken screw and buy something else. In all honesty, not recommendable for anyone if precision is what you need., consider the barrel mount instead.
Pros:
Nice looks.
Hides under the scope.
With both eyes open, can be seen when aiming through scope.
Cons:
Hard to read due to small buble compared to the sidelines
Picatinny installation is horrible quality.
Not reliable when opened and closed repeatedly.
Calibration does not work as intended.