Pre order there will be a storage upgrade. A case and screen protector.
You will be able to claim for the Galaxy Watch 6
If you pre registered your interest, apparently you can get a £50 off code/ voucher.
As for the trade in, we simply don't know yet. Find out tomorrow.
Something like the black Friday event. It really depends on what each retailer does. Some do really good deals
But I think pre orders are the better deals myself