The pet store people ... Um...
There are differing opinions. I made my own divider with plastic craft mesh, The fish can see each other but I also planted some plants right against the divider on both sides so they can have their privacy. And after a while they just totally ignored each other, they absolutely do NOT exercise anymore with each other. They will get de-sensitized to it which is why I think the clear ones are totally fine.
Whatever kind you get, make sure it has holes for water flow. It might be cheaper to make one using this tutorial :
http://www.tropicalfishkeeping.com/d...ividers-21866/