Stofen is designed to bounce the light from the flash head in all direction so that the light can be further bounced to the subject via the ceiling, walls and floor (which ever is available). If you use out door, then the only effect it has is that you will hit the subject direct plus the bounced light from the floor (if the floor condition is good). This may help to fill some shadow under the neck if the direct flash is too harsh...
anybody that uses direct flash with stofen for outdoors?