Might add some value to your house, LOL. But at the very least be a lot better than the grave in the ground shelters they sell as tornado shelters. Just need to make sure you build a sealed room that has the ability to run a generator and keep the exhaust out of the main area and some batteries for initial power with a decent inverter.
Then again he was told if he was to sell it he would have to list it as a bunker with a house attached which tells me it's probably worth more than the house so plan on taking out a loan to build it as well.