No. Stress boxes are really powerful, and far outside the scope of what Mortal Stunts should be allowed to provide. They allow you to entirely avoid Consequences and being taken out. A Stress box is flat-out better than a Mild Consequence, and it's already been established that a Stunt will only give you a single Mild Consequence.
And, that being the case, I don't think supernaturals should have access to them either. Supernaturals are alot of things, but not flat-out more strong-willed than humans, at least not inherently.
Also, from a rules balance perspective, everything in the way of Stress Boxes gains except for Hulking Size (which has severe downsides of it's own) has a Catch. You can't really give a Catch to Mental or Social stress bonuses very well.
In the rules balance area, there's also the fact that there are Weapons and other Stress bonuses to physical combat, and almost none to Mental or Social combat (Incite Emotion being a notable exception), making Stress boxes much harder to overcome there.
Also from a rules perspective, if purchasable more than once, you get really broken things, like the starting character with 10 Social Stress boxes.
