Use these quite often as my local airport is a BE hub - for reference they can be used on any BE flight with availability, not just BA codeshares. Sometimes (in particular from foreign airports with low/no APD) can be as cheap as RFS on BA too.

My last few seem to have booked into FlyBE "F" bucket, fare basis PAFM01. Definitely not First on board though!!!

Also worth mentioning that redeeming BA Avios on BE always seems to include a free checked-in bag as well, despite MMB suggesting to the contrary.