I recently got a SA gas block to tame a severely overgassed 300BO barrel. In bypass mode, I wasn't able to get it to bleed off enough gas. What I was trying to do was open it all the way up and induce a failure to lock back on an empty mag. My intention was to tune once i reached failure to lock back. I was never able to do this, even with an H3 buffer, when in bypass mode.
I then switched to restrictive mode and was able to tune my upper. I then went to count the total number of clicks so I'd know where I was. After just the rounds fired to tune, the gas block was already exhibiting signs of getting locked up.
It appears that restrictive mode is less desirable than bypass mode and bypass mode is intended to fine tune a gas system, not correct for a real overgassed situation.
I swapped to an aero precision adjustable. Much better. The SA was a waste of money for me.