BA F is often considered "J+" - their cabins are notably large/dense, although I think the A380 and 789 are supposed to be better. Still, not sure I'd pass up the opportunity to fly in the nose of a 744. Service can be variable (and without going into too much OT detail, it can depend on which flight attendant union operates on the route), but it can be great. And the Concorde Lounge in LHR is nice (though frankly, compared to the VS Clubhouse the only main advantage is probably higher-end alcohol). And frankly the Upper Class Channel is probably a better airport arrival experience than BA F, especially when coupled with an arrival by car.
That said, the surcharges on BA F (and J) awards are absolutely bat-dung absurd, probably $1500 r/t for this itinerary. Plus the miles. That's one of the reasons it's not so difficult to find availability.