A pressure cooker is enough hotter to kill many more bacteria, and green beans are one thing that's notorious for botulism, a tasteless, undetectable but horrible poison. That said, my mother and grandmother used only the waterbath method for many years and no one ever got sick. You should look at a USDA certified site for recommendations, just google canning green beans, most all county extension agencies will also have guidelines...
I don't know what I'd do, I might risk my mom's and gmom's methods, I might not. Hot water bath method is primarilu for pickles, pickled
peppers, and tomatoes and salsa. even so, the Fed. says how much acid in the form of lemon juice or vinegar to add to ensure high enough acidity. Only high acid foods are officially sanctioned for waterbath canning.