There are positive and negatives to the Miles One program.

Positive: You're not tied to a specific airline. There are no blackout dates and there are no capacity controls. The ticket is a revenue ticket and will earn miles and be eligible for upgrades, etc, if you have status on the airline you fly.

Negative: 28 day advance purchase and Saturday night stay often required. Dollar amount restrictions on the free ticket but you can choose a higher fare and pay the difference. High "mileage" schedules for Hawaii, and really high schedules for Hawaii-Europe if that applies to you. The "miles" you earn expire after three years. You have to book through their travel agency (Cendant?) which is not necessarily a negative, but you may not be able to choose your preferred routing and airline. (I was, when I used these long ago.)

The schedules used to be better for this card. Particularly they offered a reduced "mileage" zone award, where the US was divided into three zones. Travel within a zone was a bargain. (Example: NYC to Florida or Seattle to San Diego were both within a single zone.) I'm not sure if they offer those awards anymore.

At one point, long ago, under the old schedules, I used one of these "free" tickets for my step-daughters flight from Honolulu to Tampa. I had a revenue ticket on UA and was able to get her "free" ticket on my flights and she was able to upgrade with me. It saved me $800, she got miles, she was able to upgrade on my status. The first flight was HNL-ORD on a DC-10 .. a very long flight.

-David