We just took the National Coach from Heathrow to Southampton. Worked fine. Just a little hard to find our bus. Turns out the bus front says the END stop and we didn't know that Southampton was not the end stop. So we almost missed our bus. Definitely take the option to change bus time. On the Sat before our Tuesday flight, BA cancelled the flight. So we had to change all flight plans. Got in same day but different terminal. You can change time BUT NOT terminal. So we had to schlep our luggage to original terminal spot. When we got out (near the big mall), there was only 1 cab but a bunch of people wanting a cab.