Thanks chaps. The Carpe Iter is a very rufty tufty tablet so it has been ideal for trail riding. I have DMD on mine and also various free mapping apps. It's great for recording routes then saving them for future use, creating GPX files of routes that can be shared with others, importing GPX files to install routes etc.
I can see how a CarPlay/Android tablet would be ideal for mirroring my iPhone so I can use Google maps to navigate, for example. I'm not fussed about audio - I just want a big, bright screen in front of me that shows me where I am and where I need to go!
The latest Carpuride (W702 Plus) can use offline mapping and gpx files, so it's close to what the Carpe Iter will do, but it's £300, in which case I might as well buy a new mount etc for the Carpe Iter and use that.
I noticed from an older post there's a comparison of them all on YouTube, so I'm going to watch that.