Heating and filtration are still able to occur evenly when the tank's divider is perferated (has holes) large enough for water, etc, to smoothly pass through, but not bettas :D
This is mine! :D I just set it up. Im getting new plants later today!

Maccie's side:

Part of Alle's:
*Whooops. Mine's a modified TopFin Divider Kit (10 gal), I used the bindings and top claps, but not the mesh, it wasnt long or tall enough for my slightly larger than normal width tank. I used Some cheap crocheting mesh from a craft store in its place, its prettier and IMO stronger..