Would have thought USPC is most relevant for premium traffic.
Relatively less price sensitive, more time and convenience sensitive.
USPC greatly improves the predictability of end to end timings.
If nothing else, premium traffic willing to take a connection via LHR today may be less willing to do so tomorrow.
It's one more reason to be on the non-stop from MAN.
I think that's a benefit worth having.
Price is differently key at DUB, while premium traffic is doing very well, pricing still pays a big part of getting those seats filled.
Most people booking a flight don't give a taught to immigration processing times. It's a good perk but I can't see people for example opting for DUB over LHR solely because of it.