The free demo is the exact same as the PlayStation 3 and 4 version, and you’ll still be able to bring your character from the demo into the full version of the game if you choose to ever pick it up. Your progress is saved within Bungie’s servers rather than throughout hard drive, so as long as those are running, you character will always be around.
The demo is also quite large. The Xbox 360 version, known as Destiny Demo is 6GB, whereas the Xbox One version, known as Destiny Trial rocks in at a monstrous 20GB. Keep in mind you can’t store this on an external hard drive either, so you’ll have to have a large enough one to support it.
As mentioned before, I am up to my ears in Dragon Age: Inquisition these days for a review, so Bungie is going to have to wait. I’d really like to finally go hands one with Destiny though.