Even if that theory is flawed I still won't use anything like that in my planted tanks. My duckweed disappears when I have water movement, and while it is fairly easy to come by, it isn't something I should have to buy more than once, it is a weed for goodness sake! My frogbit does okay with some slight movement, but it grows so much better without it.
Of course in my personal experience, everything seems to grow better without water movement except by fish, but maybe there is some other factor I am not considering? Like the increased movement helps the BB thrive thus breaking down nutrients (ammonia/nitrites) that the plants could use to grow?
Remember that the tank your fish lives in is his or her's whole world. Ask yourself this question, and answer it honestly: would you choose to live there?