The differentials seem to vary significantly. It's not going to be an easy case of justifying Flex benefits for a reasonable surcharge to the corporate travel dept. As with others I'm now in an uncomfortable spot since my company seems to have configured lowest only in Concur. Previously I would finalize trip plans within a few weeks of travel, so almost always in flex. Now bookings in that time frame are not much different in price to low flex previously, but in Tango...