The issue I'm having is choosing which Facia kit to purchase, as there is a fitting kit of some description included with the head unit. I have found 2, one is twice the price of the other but it doesn't specify what is included, the images show a cage in one... I would grateful if someone with more knowledge would be able to tell me which one I need to buy;
As you suggest the more expensive one has a cage it also seems to include a facia surround for a top level display.
If your car has one of those I'd imagine you need the more expensive kit.
I used Connects2 facia adapters, ISO loom adapters etc. when updating my Golf - they're decent quality. You'll find them all over eBay.