Before signing up, you should check how the fine print will apply to the specific flights you typically take from the typical airports you use. Amex Plat gets you lounge access to an airline's lounge only if you are flying on that airline's metal. For example, if the lounge in your gateway city is operated by Airline X and the flight is operated by Airline X (not codeshare with another alliance partner), then you can use the lounge. So, if you're flying Delta but the lounge is operated by NWA, then you can't access either the Delta or NWA lounge.