In normal use, the internal ribs/shaft of an umbrella-style softbox generally do not create visible shadows on your subject. They can be seen if you photograph the softbox itself or catch a direct reflection of its front surface, but their effect on the actual lighting is usually minor.

Light across the front diffusion panel is typically uniform enough for practical photography. There may be some variation across the face—roughly on the order of a small fraction of a stop to about half a stop—but this is usually not significant in real portraits or product shots.

If you want the most even spread, anything that helps the flash fill the softbox more broadly can reduce visible internal structure further. For example, using a diffuser on the flash head can help the light bounce around inside the box and smooth out hot spots.

One practical limitation noted by users: some umbrella-style softboxes restrict tilt when the flash is mounted inside, unless your stand or bracket gives extra clearance.