just as an update as I'd posted about Finnair and HEL as alternative to LHR, had some recent experience: worked very well, the transit can be quite quick (on the way back I had 50 minutes between my CDG flight landing and the SIN flight taking off and both the luggage and I made it. No hassle with the passport control when changing zone. The "first" lounge is on the non-schengen side, i.e. where you land from SIN. The lounge dragon will try and tell you to go to the schengen side, which has no "firts" lounge, but you can insist to stay there, at least if WP / OWE I think. Showers were OK, food and bar decent though not above QF business lounge in AU. Looked like decent alcohol selection with local beers and spirits, but not so tempting at 7AM
Service on the flights was fine, the 350 is really less noisy than the 380, the J seats are like CX - maybe a bit narrower? I prefer 1-2-1 to QF's 380 2-2-2 in any case. The food service is "all on a tray" with what you order
(I think you can get reindeer if you put a pre-order before flying?). The food was good, they have a special gin and tonic with local berries which is not bad.
Service is to the point, but as both SIN-HEL and HEL-SIN were night flights, I didn't want to stay up and chat anyway. And they provide slippers - which I then used on QF

No PJs, but I'd brought my own (from Etihad, I thought I'd not rub it in with wearing QF branded PJs

)
Downside:
- in CDG Finnair is in terminal 2D, meaning no access to the BA/QR lounges, just a generic small lounge. TVs were showing the world cup games so I didn't mind too much

- IFE is quite limited, some recent movies but if you fly a bit you'd have seen them, TV series with just 2-4 episodes, no music albums just "radios" with themes (blues, rock, etc). QF has improved a bit on that side with the TV series "boxsets", quite good to follow a series flight after flight.
- 4-5 hours wait in SIN to HEL, 3 on the way back. As the SIN-HEL flight leaves after the QF rush, if using the QF lounge the last couple of hours are quiet. And on HEL-SIN you arrive before the QF flights, so can quickly get a shower. Should try BA/EK lounges next time.
SC-wise, as I had a booking MEL-SIN-HEL-BRU-MAD I earned 360SC, more than MEL-SIN-LHR-MAD I think as HEL-BRU and BRU-MAD were 60 SCs each in J.
On the way back I got CDG-HEL-SIN-MEL, 300SC, same as BA for CDG-LHR then QF LHR-MEL on discount J I think? CDG-HEL is 60 SC, HEL-SIN-MEL is 240 SCs.
Overall good experience, would be worth looking at that routing for personal travel if not having to go to London, and/or wanting to visit Helsinki, with your own IFE though if taking day flights.