It Pays to be Careful
If you are planning on purchasing a new pressure canner it is logical to assume that buying a bigger canner will speed up the process by allowing you to can more at a time. Be careful with such assumptions.
These units, of course, can be used for both canning and pressure cooking. Such a dual purpose appliance can be wonderful, but check out both sizes and capacities. In other words, with some models you will find that you can increase the quantities of food going into the pressure cooker, but as a pressure canner the smaller sized unit will only hold 7 quart jars, while the the larger sized model will still only hold 7 quart jars. It may, however, fit more pint jars than the smaller canner, but will you be using pint jars?
Yes, studying it out before the purchase can be a good idea. Bigger is better if bigger has some advantages for you, but you need to determine if that is really the case.