I'm just gonna give you a fair warning about duckweed from experience, if you have the average intake for your filter, like the HOB filter, your duckweed can easily get sucked down towards it and clog the intake. This mostly happens when the duckweed is pushed down by the output, too. It's incredibly annoying. I ended up putting a filter sock around the intake, so that the duckweed wouldn't get sucked up by the filter, but every week turned into every day cleaning the filter sock because there was just so much duckweed! So I tried a different method... I had some spare suction cups and some airline tubing, I wedged the ends of the tubing into the hole of the suction cups and attached it inside the tank right at the surface line going across the tank from back to front to work as a bouy or guard line to keep all the floating plants away from the filter. More complications bloomed from this though. One, I would find myself constantly adjusting the tubing because the water line was always changing. Two, airline tubing is too flimsy and gets really gross looking, I ended up switching to CO2 tubing which I found a lot less flimsy and a lot easier to use. Three, since the tubing is at the water line, it makes the water still and eventually protein film will begin to form.
I got so tired and irritated from floaters that I ended up getting rid of it all, I got so fed up with it. I love floaters, frogbit is probably my favorite floaters, they're very attractive, but unless you have a sponge filter and smooth water, I wouldn't recommend floaters, it can become such a pain to keep. However, the floaters can really make your display look very pretty, even with the guard lines stopping the plants, sometimes a small current would sneak through and make the floaters just calmly spin in a circle around the tank, this helped with the protein film but most notably, when the moon lights came on, the shadows from the plants while they were going in circles gives such an amazing and natural look on the tank!
Floaters are also typically considered nutrient hogs, not entirely sure about duckweed, but a lot of people say floaters have helped with excess nutrients to keep algae from growing, but also hogging nutrients from other plants as well, which I don't think will become a problem really.
So there's some pros to floaters, but a lot of cons.