American Express is offering a 35% bonus on transfers from Membership Rewards to the Air France KLM Flying Blue program between September 10 and September 16, that’s one week only.

The page to transfer to Flying Blue now reflects the transfer bonus.

For flights in coach or business class departing the U.S., Delta is usually the better American Express transfer partner. Flying Blue adds fuel surcharges to awards whenever paid tickets would include those charges, while Delta doesn’t on most though not all partners (but does add an international origination surcharge, so if you’re beginning your trip in Europe Delta may not turn out to be the better option).

This 35% bonus may compensate for the fuel surcharges that the Flying Blue program adds on to awards.

There are other advantages as well. Delta frequently has IT issues ‘seeing’ space on Air France that’s being offered as an award. The Flying Blue award redemption website is quite functional, whereas the Delta website only displays a few partners and is glitchy. Flying Blue also offers first class redemptions, whereas the top cabin offered by Delta is business class. Although only Flying Blue elite members can book first class awards on Air France.

Air France KLM Flying Blue also offers one-way awards at half the price of roundtrip, which Delta does not. And they offer ‘promo awards’ which allow you to fly between certain cities (which change every two months) and anywhere in Europe that Air France or KLM flies for half the usual points required.

I like 35% bonuses, not as much as 40% or 50% of course. What I don’t love is that the bonus lasts only a week. I wouldn’t transfer points out speculatively. I like my Membership Rewards points primarily for their flexibility. I can move the points wherever they need to go when I know that I need them somewhere in particular to redeem for a specific award. I don’t really like the idea of giving up that flexibility for a 35% bonus, since I may find later that I would have preferred to move the points somewhere else.

But if you have an award you’re looking to book, and it’s possible that Air France KLM’s Flying Blue program could be the way you’d make that booking, then looking at making a reservation this week in order to take advantage of the 35% transfer bonus could be a good idea.