Actually the RAF saved the UK from invasion by the Germans, at least in 1940. Hitler was impatient and went off to invade Russia the next year, then, on top of that, declared war on the USA, thus doubly dooming his chances of ever winning the war.
These dry ice bombs are NOT totally harmless. If a piece of sharpnel from the plastic bottle would fly into your eye, or lacerate the skin of an exposed body part, it wouldn't be too funny. But that's just the R.N. in me thinkin'.
I wonder if NASA would consider opening this up to the public. There would be a lot of people out there who'd pay big bucks for using this for, say, and hour. I wonder if they could make it simulate a F-22?