Softbox for Flash
Since you are asking about using a softbox with your hot-shoe flash for portraiture I assume you are trying to get soft light. In that case I wouldn't recommend any of the tiny softboxes you list.
For soft light you need a diffuse source of light that is large with respect to your subject. Practically this means you want a diffuser for your flash/strobe as big or bigger than your subject and you use that diffuser at subject to diffuser distances of 1 to 2 times the diagonal/diameter of the diffuser to get a good ratio of highlights to shadows across the subject.
For a waist up portrait you are looking for a diffuser in the 32" or larger range. A 32" white umbrella with a removable black backing is one good choice but I would rather have a larger diffuser myself.
Here is an inexpensive 42" diffuser (about 40" diameter) that will do what you want. The build quality is acceptable and if one gets knocked over or blown over and ruined it is cheap enough to be considered disposable.
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