A transfer between Munich Airport and Düsseldorf Airport covers 614 km in around 5h 55. It exists for the day the connection breaks — when the replacement flight leaves from a different airport and getting there is suddenly your problem rather than the airline's.
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 terminal door, not the car park. 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 Cologne Bonn Airport, priced the same way.
Luggage stays in the car for the whole 5h 55, which is the single biggest practical difference from any rail route: nothing is lifted onto a train at Munich Airport, off it again at the interchange, or onto a second one for the run into Düsseldorf 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 55
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 55 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 Munich Airport and once at Düsseldorf Airport, and the rebooking calls you still have to make are easier from a back seat than from a platform.