As far as gssf and other competitions, do more shooters shoot with one or two eyes open?
Shooting both eyes open for me is extremely difficult.
Do you know your eye dominants? I shoot right handed, but am left eye dominant.
This was a hard obstacle for me to overcome, I ended up switching to XS big dots sights which helped out a lot. After about a year of shooting with both eyes open I can shoot notch and post sights, but still prefer the big dots.
If you are cross eye dominant, my suggestion would be to just turn your head until your dominant eye lines up with your sights. This is pretty easy when you are just standing on a square range, but it gets harder when you start to shoot around cover, and at odd angles.
My biggest problem was when 3 targets where set close together I would start to see doubles of the targets, and then close my right eye and my sights would not be on the target. This is where the big dot helped the most as the front sight is so big it really catches my focuses.
In the end if you can make it work I think you will be a much better shooter with both eyes open.
Edit: If you are thinking of trying XS big dot sights, see if you can find someone with a set you can try out as a lot of people don't like this type of sight. I am not one of these people who think they are the best sight out there, but they do work well for me.