Any form of diffuser has to be good for taking pictures. Using a diffuser 'softens' the light so that shadows are softer edged rather than sharp black areas. The problem is that simply diffusing a light source is not as simple as it sounds.
To be effective a diffuser has to be as big as possible. In portrait/fashion work, a popular light source is a 'Soft Box'. A soft box is a square cone, like a pyramid. The flash light source is at the sharp end with the flat base of the pyramid being made of a white diffusing material. These soft boxes range from a couple of feet square to six feet square. When light is shot through a diffuser, the diffuser becomes the light source. Given that to be effective, the light source has to be a large as possible, I would be looking at a frame of around A3 as a minimum and to keep a reasonable distance from the model. The light has to be far enough away from the diffuser to ensure that the whole diffuser surface is used or it will only be diffusing a small area of light passing through if the lamp is too close.
I have seen, and experimented with, small diffusers that fit over you 'on camera' flash gun usually a simple bit of white plastic. These do virtually nothing other than reduce the power of the flash as the diffuser is small and very close to the flash gun. In this case, the size of the light source is unchanged and so is the effect.
For models, the best diffusion is probably a small to medium light tent with lamps coming in from the top, sides, back and front. This will give the softest light possible but is probably not worth it unless you are doing catalogue shots. A simple home made light tent can be made from a large cube cardboard box. Remove the lid flaps from the box so it is open topped and turn the box over so that the open side is on the bottom. Mark a square on each remaining sides and top but not the back so that a couple of inches border is left and cut the squares out. You should be left with a box that is open at the bottom, frames for the front, top and two sides and a solid back. Cover the two sides and the top with tracing paper. get a sheet of thin card as wide as the box and long enough to run from the bottom front edge to the top rear with a curve as it goes up the back. Place your model on the curved background and place lamps one to each side and one from the top. Again, don't get the lamps too close or it will reduce the diffusion. Place your camera pointing in the open front and shoot away.
You can move the lamps around to get some detailing shadow, for example have the left light further away than the right lamp and you will get a bit of shading forming on the left side.
That is probably a rubbish description but it is getting late and I am tired lol. Any questions, as away.
