Faster explosives generally deliver a more cutting effect due to the fast moving wave but the energy is also extremely short lived as one would expect. Fast explosives in a "shampoo" bottle as I have heard this one described would result in exactly what we saw. A pliable plastic container would not allow the energy released to build adequate pressure in the vessel prior to the secondary energy release... so all you heard was the shampoo bottle pop and all you saw was a guy running around with his nuts on fire.
Had this been contained in a more stable container, the result would have been exponentially more damaging relative to the rigidity of the container or if the container was designed in a fashion to direct the secondary energy release and focus it in a specific direction.
Slower explosives tend to expand slower (of course) but are also capable of much more expansion on a relative scale. They will deliver the energy further from the ignition point.
They had a workable idea but the shampoo bottle would have never delivered the damage they wanted
You know, while reading your explanation (BTW, thank you!) it all comes down to rudimentary physics. It seems a MecE should know those things.