I got two of the frames in my room, each with an Eco Black and Hofa Diffusor. With the other self-made absorbers in 4 corners and 2 edges of the room, I am happy with the result. Depends on your room size, but probably one of these frames alone wouldn't do the trick yet, rather at least 2 or more plus other acoustic treatment.
Building quality is good, though the modules themselves could be a little bit heavier, to be able to absorb more room energy. You can see some dried glue where they put the wooden parts of the frames together, but that's not an issue for me.