I suspect a "cobalt bomb" would be less effective in terms of explosive yield than an equivalent normal multi stage weapon design - the neutrons from the fusion

I suspect a "cobalt bomb" would be less effective in terms of explosive yield than an equivalent normal multi stage weapon design - the neutrons from the fusion reaction in the secondary being used to activate the cobalt rather than into fissioning the fissile jacket of the secondary where most modern weapon designs actually get most yield.