There are a number of "mini-softbox" products on the market. These are meant to mount on a hotshoe flash (usually with an elastic band).
Are these worthwhile portable and low-space light modifiers, or are they more gimmick than useful? Are they large enough to meaningfully diffuse light for portraits? Are they too close to the flash?
What are the use cases that these are especially good for? What can't they do?
Are any particular designs better than others?