I also have it in my 40G breeder tank and it grows so much, hand fulls literately, I bought $2.00 from my LFS and took off so fast is great for fry and for big tanks and the way it looks is really nice.
I feed my goldfish, rainbow fish and American flag fish and they love it.
I have HOB filters on all my tanks and I use aqua clear sponges to make cover for the intakes, try it in one of your tanks to make sure you like since not everybody is fond with it.
We;; what I do is get a mesh that has smaller holes and cover it that way.
Get some of the egg-crate plastic diffuser (used for florescent lights, Home Depot sells it), plastic canvas (used for needle point, hobby store has it) and some model glue. You can use needle nose pliers to break/cut the egg-crate to make the sides of the wall (only need front and 2 sides) do a rough fit and glue with the model glue (when it dries and cures it is safe for fish, have used before) Build a box around your overflow, about 1 inch away from its front and both sides. extending 1 inch above water 1 inch below, not up against the "teeth" of the overflow, need room to prevent the duckweed from getting gummed by the flow of the water. Make a notch in the back of the box so it can rest over the edge of the tank, to hold itself in place.
Cut the plastic canvas and mount to the box to stop the duckweed from entering the overflow (I used zip ties), again extending 1 or 2 inches below the water and an inch or so above (low enough so the floating duckweed can't go under or over)
The plastic egg-crate gives a strong structure, the plastic canvas stops the duckweed getting close enough to the overflow, but allows the water to flow easily. Can spray pain the box with black acrylic spray paint to help and hide it, just let it cure a few days before use
Hope I was able to describe the little build properly, have built these little screens around my skimmer before, worked well
I have duckweed in all my tanks, it looks nice and helps to keep my tanks balanced, I have HOB filters, I do use sponges in the water intake so no duckweed goes in the filter.
A friend of mine gave me literally like 10 pieces of it and in 2 months I have it in all my tanks, maybe eventually will hate it but for right now I really like it and enjoy it, my goldfish eat it.
If you have a local fish store, they probably would be happy to get rid of some of their duckweed for free. I would use a screen, and angle it away from the overflow, so the duckweed can't get too close to be violently pulled at it.