I think the trial is more confusing than anything else. I've been on flights where others have reported to be offered a free drink and I haven't been offered a free drink. I don't care but I just want to point out the inconsistency that is IMO more annoying than anything else.
It was similar when group boarding was introduced on some both not on other Flights. Even today where group boarding is more or less being done everywhere, there are still passengers and ground staff confused about the concept.
Moreover, the idea adds yet another layer of complexity to the whole BOB system. On a recent flight to BRU, it took them nearly the entire flight to charge my seat neighbour's credit card. The service was overall slow and they spend a lot of time with each passenger that tried to order something.