The 565 km between Düsseldorf Airport and Berlin Brandenburg Airport take roughly 5h 27 by road. Booked as a transfer it is one vehicle from one terminal kerb to the other, at a price agreed in advance — which matters more than usual on a day that has already gone wrong.
The pickup is driven by your inbound flight number: the driver watches the actual landing time and waits 60 minutes free after touchdown, which is what a diverted or delayed arrival needs. At the far end the drop-off is at the correct terminal for your departure — Berlin Brandenburg Airport has 2 and the wrong one costs a shuttle ride you do not have time for. Tell us the departing flight at booking and the schedule is worked backwards from its check-in deadline rather than forwards from a convenient departure. We run the same journey to Hamburg Airport, priced the same way.
Luggage stays in the car for the whole 5h 27, which is the single biggest practical difference from any rail route: nothing is lifted onto a train at Düsseldorf Airport, off it again at the interchange, or onto a second one for the run into Berlin Brandenburg Airport. If the airline has rebooked you and is reimbursing ground transport, the invoice shows the route, the date and the fare in a form an airline will accept.
What you are committing to at 5h 27
If you have read the comparison above and still want the car, this is what you are committing to. One driver and one vehicle for the whole distance — no handover, no change, no platform — and a comfort stop wherever you ask for one, which on this length most people use once. The reason people choose it at this distance is almost never comfort. It is that across 5h 27 no gate closes on you and there is no second boarding pass to lose: the deadline you are driving towards is the only one left in the day. Your luggage is handled exactly twice, once at Düsseldorf Airport and once at Berlin Brandenburg Airport, and the rebooking calls you still have to make are easier from a back seat than from a platform.