I quite like the Flagship lounge access as I almost always go through DFW. Polaris was only just announced when I left UA but I would say the limitation to GS on international business is a negative compared to AA. I use Flagship on domestic economy a lot and enjoy being able to get something better than lentil soup for a meal even if it's not the full Flagship Dining. +1 CK
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This is one of the perks that really gets me as a GS. I wouldn't mind being able to bring in guests to the UA lounge. I would also think that allowing GS to have polaris lounge access regardless of cabin/destination would be a nice perk as well.