I've not travelled through T5 and probably won't as BA is not my airline, so I won't comment on the various fiascos, those utter failures of preparation and planning.
I've never understood what the attraction of the post-security shops are. There is no more duty-free. All they seem to do is hamper progression from security to the gates, so I usually get to glimpse the pricing. Unless the goods at them are actually cheaper then in peoples home countries - why bother? - and aside for possibly Scandinavia, I can't really think of anywhere where they would be cheaper. I laugh when I see the prices. Actually laugh.
I buy real duty-free onboard the flight home and save about 50% over the crap offered at LHR. I might buy a chocolate bar or have a cheeseburger at the pub, but that's it.