Yep, as a long term FFM collector in several schemes over the years:
- Never change your buying habits to acquire Miles
- Never buy Miles form the carrier - unless you just need the odd 1000 to complete a deal
- Use Miles for upgrading
- Best use of upgrades on long haul only.
- You will pay taxes and charges and, with some carriers, these can be very high. On short haul, it's always best to go with an LCC or even main line, than to use Miles on a main line.
Buy an upgradeable Y and then use the Miles as this is the most cost effective use of them. You get a better deal coz the carrier has got some hard cash from you. I have had to use Miles for the full purchase and it is uncomfortable.
Also, consider using an LCC to your European transit point, then Miles from there. Of course, this is two separate tickets so an extra lay over time is needed.