Thanks! I was able to book through Kayak -> Uptravel. The PNR was ticketed in about 30 minutes after and both AY & BA show fare on their website, earning 160 TP and about 3400 avios.

However, no option to select a seat, on either website or Finnair App (anyone got this done?).

Fingers crossed for now equipment swaps. For the rest, amazing fare, having been AY-ing to fly this route on the A350 for a while now. Previous strategy was eco fare + upgrade with miles one way, but at this price point it's a steal considering it's for the RT. Adding to that is that there's a wonderful variety of OW lounges at LHR to enjoy and lounge at HEL is no punishment either. Thanks again for posting this!