First saw these things late last year. Absolutely awesome!
They are equivilant to a stick of dynamite, I think, but it takes a lot to set them off. We hit one several times with a 9mm +P+. Nothing. .223 round? BOOM!
If you haven't tried Tannerite yet, you just GOTTA! If you do more than one, it wouldn't hurt to let your local LE office know so that when their phones start ringing, they won't think WWIII has started.