It allows you to get any available seat on any flight, but you'll pay a premium award rate tied to the current cash price of the ticket. (rewardexpert.com)
These airlines have revenue - based frequent flyer programs, so calculating the cost of award flights is not possible, since redemption rates are tied to the current cash price of the ticket. (rewardexpert.com)
Award prices can be estimated with the Flying Blue Miles Calculator, however actual prices will fluctuate with cash price of tickets. (upgradedpoints.com)