Pressure canning is used for preserving low-acid foods such as meat, poultry, seafood and all vegetables except for most tomatoes. If not preserved properly, low acid foods can create the environment for the Clostridium botulinum bacterium which causes botulism. To prevent this, food must be processed at 240°F for the time indicated in the recipe.
Below is a comparison video on the All American and Prestor canners. I hope this video is helpful if you are still trying to decide on which one to buy.