Interesting this got posted. I played with an open bridge for some years and never got much improvement.
Recently a friend watching from the sides told me that my stroke sucks and when playing shots that require more english, I tend to miss the pockets by miles. On the last moment of releasing the cue, the wrist action and the open bridge will veer the cue to the right side.
Anyhow, on his advice, I changed to a closed bridge and viola~!!! I begin start potting better now. And whats more interesting is that after a while, I begin to pot better with an open bridge too, probably brought on by the awareness of the bad stroke previously.
So right now, I always try to use closed bridges during the first few games to help my muscle memory remember the correct stroking posture, and then gradually change to open bridge if I feel more comfortable with it. If I am starting to miss simple shots again, I will revert back to closed bridge to correct this.
I also watch a number of youtube videos to observe when does the pros use close or open bridges and the ratio i gather comes close to 80/20 ( closed/open )
my 2 cents