Finnair, a oneworld partner along with British Airways, is offering a 50% bonus when you transfer in points to its Finnair Plus loyalty scheme.
This includes American Express Membership Rewards points which transfer at 1:1.
Any oneworld redemption you can book via British Airways is also bookable via Finnair Plus. However …. Finnair has its own rules regarding the miles needed for flights, the taxes due and cancellation rules.
You should not automatically assume that it is suddenly a better deal to transfer Amex points to Finnair to redeem for a BA flight. It might be but the answer will vary route by route and class by class.
Finnair has two hotel transfer deals – to Accor (click here) and to IHG Rewards Club (click here). I have done the maths and, even with a 50% transfer bonus, it doesn’t make sense to me to go Amex to Finnair to Accor / IHG.
If you want to explore this a bit, full details are here on the Finnair site. You must register by 30th April and transfer by 30th June.