Thank you, I had spent much time squinting at the TFL site and thought there was no reason not to get the Oyster card, except perhaps the deposit, and possibly leaving money on the card.

That's why I thought it was worth putting enough on the Oyster card to bring it up to an Off-Peak Day Travelpass (-50p) each day, rather than a large amount up-front. That would be £5.80 on arrival at LHR, and £4.40 each day thereafter (assuming I stay within zone 1).

It appeared that while they were pushing external sources of cards and top-ups, that you can still buy the card at a ticket window, and do the top-ups at the ticket machines? Would I have to know I need £4.40 or is there a "Off-Peak Cap for Zones 1-2" prompt?

Oh, and will it let you exit the system with a negative balance? Washington's Metro does, or did when I got a permanent card in 2001, since they know you'll be topping it up again eventually.

Thanks!
=aw