I just did a food shop with brompton as trolley, which is probably about the 5th time I've done the trolley thing. It was a pleasure today, perhaps partially because I'm a bit better at maneuvering it, partially as the shop was fairly empty so I didn't have to be to vigilant about not bumping into people. Left the shop feeling extremely happy and bonded with the bike.
Flex aside there's something I particularly like about the way it rides too. And I even managed to carry both bike and full basket up a flight of stairs (1st floor flat) without touching the newly painted walls. I'd previously been doing two journeys which rather detracted from the utility of the thing, and was thinking I'd probably have to sew a shoulder strap into the folding basket so I could use two hands to carry the bike. Perhaps I don't need to.