As an AY Plat (or any other metal, really) I avoid the hell called LHR transit, F lounge or not.

Next week I'll have my first ever CX longhaul HEL-AMS-HKG-TPE in C and back in PEY. Matrix priced it out, but no OTA capable of selling it, no issues for real-life agent. I'm quite content to fly and try the CX PEY product on a day flight - for night flight I prefer the C for a good sleep (and to compare CX A350 vs AY A350)

(I would've chosen AY, but for their crazy pricing for HKG and even crazier for TPE even ex-EUR)