I had the store bought dividers originally, but went to the craft store and bought black cross stitch screen. Great flow through the screen with very limited visibility to the other side. Mine have no idea what's over there.
I still use the frame from the original divider I bought in the store.. the pennplax ones.. but I have since then used craft sticks. They're basically just popsicle sticks that haven't been used for popsicles. I silicone two together with a very small piece on the ends and then slide the cross stitch mesh into the small slot it leaves.
Plus there's always the plastic with the holes drilled(doesn't have to be clear).. but I'd be worried about flow.