IT was still hackable on the earlier mavic models (up to Mavic 2 Pro i believe) and yes it was very useful.
I often used it to judge actual wind at altitude (take it up, put it on ATTI and you can clearly see the exact wind direction and speed...
It's a shame that Atti mode disappeared with the Phantom series, I enjoyed flying with it with both my P2 and P3. The P2 did have a full manual mode which was crazy.
Flying and Recording Video are two VERY different things. I learned video skills decades ago with my camcorder. Some home videos are painful to watch due to jerky sudden movements and simple lack of planning. These skills also apply to...
I had to first confirm that the mini 3 props are indeed different than the mini 3 pro props and they are different and NOT interchangeable. I'm in Canada and not the UK but a quick search shows Amazon.CA has carbon fiber props for the mini 3.