I bought these to treat my walls of a square room. I know, the worst. But these puppies helped tame the reverb/reflections I had, to a bearable minimum. Depending on your choice of method, they can be nailed, glued, taped, and hanged on the wall. Tip: next to wall treatment, use a room-correction package (software/measurement mic).
Pros: price, quality, looks.
Cons: need more.