Fundamentally speaking, diffusion panels and softboxes serve the same purpose: creating a larger source and thus, softer overall light. However, in practice, they can have different effects on your subject and can also be easier or harder to work with depending on your needs and setup. This great video will show you their advantages and disadvantages to help you decide which is right for your work.
Coming to you from Daniel Norton with Adorama TV, this excellent video discusses the differences between diffusion panels and softboxes. Softboxes are one of the first modifiers most photographers try, and they are a cheap and relatively versatile tool that you will probably continue to use throughout your career. A diffusion panel, on the other hand, is simply a piece of translucent fabric fitted to a frame. You then aim your light at it and shoot through it to soften it. These can be a little easier to work with if you do not want to deal with different speed ring adapters and want to be able to quickly move lights around and make adjustments without changing out for different sizes and the like. Both have pros and cons; check out the video above for the full rundown from Norton.Â
He's missing an integral part of using gel frames: flags/floppies. You can see numerous times when the light from head is spilling onto the background. This could be fixed with a floppy. He could put a flag/floppy as a topper, bottomer, on the sides, as needed. This could also control light bouncing around the studio.
He is also missing barn doors on the head, which would help a lot with spill.
You can also change the angle which the light hits the diffusion on the gel frame and this gives you further control. eg. You can aim the light at an oblique angle and have the light cascade unevenly across the diffusion.
There are also two other incredibly aspects of using diffusion panel over a softbox: your choice of numerous types of diffusion fabrics which change the specularity and the softness of the light. The catch light from using a diffusion panel is much more pleasing IMO then the hard edged soft box: square softbox catchlights are so obvious. You can also use different reflectors on your head to change the way the light falls off inside the diffusion panel.
https://www.leefilters.com/lighting/diffusion-list.html
Have a look at the Lee site and you'll see on the right side all of the different ways the light diffuses when going through the fabric. You can also see the affects at the top compare function. One of my faves is 410 Opal Frost.
You can also use a frame which is much larger than any softbox could ever be.
It is obvious he is not very familiar with using frames.