This is old review of this brake by WOLF@TS
Perhaps I can help you with that.
Over the last few weeks I have purchased several brakes from Corwin.
All have been used on a non-restricted length 858.
The large brake with the two top slits and the round side ports I found actually over compensated a bit on the long barrel and would probably be more suited to the shorter barrel lengths.
I am now down to these 3 styles:
Left to right...
The A1 "birdcage": More flash hider than muzzle brake. Mild reduction in muzzle climb, minimal effect on recoil (not that the 7.62 is that bad to start with) and good dispersion of gases 360' around the muzzle through 6 slotted gas ports.
The "short" Czech brake: Excellent design. Vents gases back and upwards in a shorter overall package. Looks great and almost completely eliminates muzzle rise and reduces felt recoil.
The "large" Czech brake: Very noticeable reduction in recoil, zero muzzle rise. The only drawback is the length on the already looong barrel, on a standard length or shorter barrel I think this would awesome.