TL;DR: Theres lots of energy (but less than I thought), it's probably (too) easy to release, so yep it's dangerous.
If I understand it correctly most of the energy (apart form E=mc^2 energy that can't be tapped easily) is what comes from the mechanical work squishing the hydrogen down to size.
That means the energy density should be in the order of the pressure, which is 495 GPa. So a cubic metre of the stuff would have half a terajoule of energy. Wikipedia says the Nagasaki bomb was about 90 terajoules.
If the stuff behaves in a simple way, you can release the energy by just releasing the pressure. If it is "metastable" that means it can somehow remain compressed when the pressure is released -- but will be "trying" to explode to its uncompressed state. We don't know if the metastable state even exists, let alone how easy it is to get out of.
