The pressure canners are easy to use if you read the instructions and don't get creative, nor leave the pot alone while it cooks. If something needs 90 minutes cooking time, you must stay there for 90 minutes.
Problem with substituting a pressure cooker for a canner is that the cooker has no specific pressure it cooks at, which is very important for keeping food safe, nor can you do quantities in it. Not knowing the right pressure is like not knowing if you have fuel in your car for a long trip. Guesswork doesn't cut it when it comes to food safety. The proper amount and time of pressure will kill anything in the bottles.
The canners have either dial gauges you read and keep the heat steady at for pounds of pressure, or, you set a special weight on the unit and it will self control, eg 10 lbs, 5 lbs, etc and you clock all of these depending on what you're making. The higher the pH level, the longer it needs to cook. eg a quart of meat will need 90 minutes at 10 lbs pressure if you're under 1,000 ft altitude, 11 lbs above 1,000 ft. These are clearly outlined in instruction books that come with the canners.
I never bother pressure canning marmalades, etc as they already have enough sugar and acidity to keep them safe and can be safely water bathed for around 15 minutes (provided the contents are already very hot). Some folk don't bother water bathing jams and such, but I always do for the safety factor. I make a LOT and can't count on eating it up within a year, nor two. I've had jams 7 years old that still taste like the day I made them.
Mostly, I pressure can all my tomato sauces because of digestive sensitivities. Water bathing and freezing just don't work for me, but pressure canning does and I can safely eat all tomato products I pressure can. I now do meat and butter in the pressure canner to save freezer space. They're very easy and safe to do. Check youtube for videos on them.