There are two types of ATS units that I have considered, other than the type I have now.
One is the Inland Aquatics version, which mounts on top of the tank and has the turf growing on screens that are on a hinge. The water fills up until a certain point that the weight of the water causes the screen to tilt forward and dump. I like this because it not only gives you an effective way to grow your turf algae, but it also gives you a good surge device that dumps pods and bits of edible algae into the tank.
The other is a basic surge device, using a glass or Plexiglass tank (40 breeder?) that uses a float mechanism like a toilet does. The turf screen lays diagonal from the bottom corner to the top corner of the tank and the water fills the tank from a pump in the sump. When the level gets to a certain point, the water dumps from the holding tank into the tank below. This also creates a surge like the IA version above. It is simple and quiet.
The type I have now (pictured below) was made by a company that no longer makes them. It lays flat over my sump and fuge and water flows in one side, goes over some turbulence causing baffles and then empties out the other side. Two lights sit on top of the unit. It works off of the gravity of my drain and requires no mechanical parts. Simple, quiet, and effective.