I had understood that the iPad GPS wasn't real GPS (i.e. communicates with satellites) and that it worked through the cellular system which caused map drawing to be slower. Ergo my interest in something that would talk to a satellite and then to the iPad via Bluetooth.
That was the gen 1 iPhone. Later model iPhones and iPads have real satellite tracking GPS units. However, they also use cell tower triangulation to improve the accuracy of positioning. My current generation iDevices can accurately track which room of the house I am in and do a decent job of determining the highway lane I am driving in. I have navigated across sections of the country more than 50 miles from any cellphone or data network connection using my iPad.
One advantage of the iDevice maps. They are invariably more up to date than the maps on dedicated GPS devices. Mainly because they are downloaded on an as needed, when needed basis. And because the actual routing is also downloaded on the fly, they do a better job of avoiding traffic snarls. It took one trip using an iDevice for me to get rid of my Garmin.
