I think I'll take my chances aboveground. Claustrophobia would be a problem.
A septic tank company in Pensacola had a deal to sell & install steel fallout shelters and installed one at their office. The fallout shelter company folded and the septic tank installer used that shelter for many years to store diesel. I was regulating pollutant storage tanks at the time they dug it up and it was very well built and it didn't leak.
It had wide stairs going down into it. It would have made a great storm shelter if you don't mind crawling into a hole in the ground.
We have a bathroom on our lowest floor in Hoover that we use as a shelter. We stock it with a weather radio, water, snacks, dog food (for the dogs), flashlights, and a small first aid kit. This week, a half-mile wide tornado missed us by 4 miles or so. It's scary up there. They have huge rotating sirens that could wake up the dead.