Anodizing is a process used to harden aluminum, and is done only to the outside of the pan to make it more mar-resistant. There are a good many aluminum pressure cookers out there. As long as you use it for what it was designed for, it will do its job. For instance, don't try to pressure fry foods in it. The intense heat of 360' oil will create sufficient pressure to turn your appliance into a bomb. But using with water, it will not exceed 1t lbs. internal pressure, max, which it is designed to withstand easily.
Let me tell you from experience, if you let all of the water evaporate out, and stuff burns in it, it becomes a real chore to clean. You can ruin the pan, depending on what is burnt into it. I remember destroying a pan when a liver recipe was burnt into it. I never did get the odor out of that pan.
Just follow the directions that came with the pressure cooker and it will do wonderful things for you.
Seeeeeeya; Goodweed of the North