Fotodiox6X9" Foldable Flash Softbox For Speedlights; Nikon, Canon, Vivita, Sunpack, Nissin, Sigma, Sony, Pentax, Olympus, Panasonic

What is the advantage or difference between using this or something like the Stoffen plastic diffuser on an SB-600?

pardon my ignorance, but is this kind of softbox more useful for portraiture or event shooting with the flash on and off camera? sorry for the wording

Does this softbox have wire or plastic tubing inside to help keep it upright and retain its shape? What keeps it from sagging?

Will this fit the Yongnuo YN568EX for Nikon?