Two years ago, we took our first Cunard cruise, for a pair of milestone birthdays. I had our TA book a westbound crossing in QG. When flights were finally available, I asked our TA to book specific BA flight and seats from BOS to LHR, as well as AA flight from LGA to BOS at the end of the cruise. I was monitoring BA's website and could see the desired seats being committed in real time.
In researching flights I could see that in many cases a one-way flight could be almost the same as a round trip ticket. One advantage with Cunard Air is that one can mix and match airlines and could get reasonable one-way fares. (For our next TA, I will seriously consider Amtrak Acela from NYC to PVD.) And we didn't have to pay until T-4 months.
But we had one major issue. A few weeks later, AA dropped the NYC/BOS shuttle. AA rebooked us from LGA to Ronny RayGun DC airport, and then after a number of hours, finally from DCA to BOS. Cunard Air dutifully sent us the new air booking. They also did this every time BA modified their flight schedule.
The problem was that Delta also operated the NYC/BOS shuttle. So I wanted Cunard Air to change the AA flights to a non-stop Delta flight. The only way for Cunard Air to do this was to delete all flights and start over. But when we originally booked the BA flight, we got a fantastic FC deal that was only about 20% over their idiotic Club World Business seating.
So there are good things and bad things about Cunard Air.