Hi. you can also make your own using plastic canvas [from a craft shop] and page binders [ from a stationary shop]
The plastic canvas already has holes in it, so you just need to cut it to size. Slide on the binders at the sides [top and bottom as well for extra rigidity] and wedge into place. You could use aquarium type silicon to attach the binders in place in the aquarium if you want a more permanent divider, but this needs to be done on a clean dry surface.
You can push the base into the gravel/sand to stop anything sneaking under. You can also use suction cup thingys either side of the divider, stuck on the glass, to stop it from sliding out of place.
These are very easy and cheap to make, so I hope my instructions made sense. I use these to separate my girlie bettas and they don't seem bothered that they can see each other, even though I know they fight when together.