I agree with all above.
At least with closed you don't have to think about your reins - one longer, what if I drop one, easier with one hand speed events ...ect.
I prefer split reins for pleasure riding, or reining when you would probably want more individual control.
Either way I don't think the style of rein should have a whole lot to do with a difference in asking your horse to do something - they're both attached to the bit. So a split rein or a closed rein shouldn't confuse your horse (rider maybe...lol)