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If you redeem BA miles for BA flights, you will be hit with significant fuel surcharges. These surcharges will also be imposed on TATL flights on AA and IB when redeeming with BA miles. On the other hand, if you redeem BA miles for AA flights to Japan or China, you can get very good value (and pay no fuel surcharge -- at least not currently).

Once you transfer MR points, you lose the flexibility that those points offer. And while no one can accurately predict the future, I don't think that this is the first time there has been a bonus for transferring to BA.

There is also the risk that changes to a program's redemption rates or fees could significantly devalue miles in that program.

You might take a look at AC's Star Alliance redemption rates. Even without a transfer bonus, AC offers some could deals between North America and Europe.