Had not thought of the spalling from the porcelain. But getting cut by flying chips is still better than getting shot. as to it breaking up, probably, but in that situation any hits on the tub would most likely be by accident, the BG would be focused on the threat he can see, YOU and will not be concerned with the tub, if he even notices it.
As for breaking up cast iron tubs, ARE YOU CRAZY !!! Do you have ANY idea what people pay for that kind of stuff ? $500 - $1000
Dude, You need to watch a few episodes of Antiques Roadshow !