This is my favourite flight to LHR. The red-eyes are too short for a good nights sleep. The flight leaves early so by the time you get to your hotel/home you are knackered and ready for bed. Really erases any effects of jet lag.

As for meals, in J they serve a full hot breakfast (usually omelette, bread, juice, yogurt, fruit etc.) and they have a full dinner service 2 hours before landing. Sometimes they forget to take meal orders at beginning of flight so if you want to nap make sure you tell the FA in charge what you'd like so you're not disappointed.

As for upgrades, I've been successful as an E twice on this flight in the past two years so if you're flying on the right day of the week the stars should align for you. I believe one upgrade was done at T-4 and one was processed at the gate.

Once I was flying this in paid J and the flight left with 2 unoccupied seats in J.

Never done this in Y (luckily) so can't comment on the meals.