Nice trip report. I enjoyed the part about the grumpy seat mate and you not swapping - good for you ^
The pictures are very good and the T5B lounge looks nice ,but not nice enough for me to leave the CCR and go across there, as all my long haul is in F
The only time I could possibly see me using it, is on a CE flight departing from T5B but then I suspect it will get a lot busier and wouldn't be as pleasant as when you visited, so it's probably best to stay in Galleries First in T5A.