Medallion, regardless of whether its FO or DM, has both tangible and intangible benefits. I qualified at the end of 2009 and was FO for 2010-2012 before hitting GM at the end of last year, and am going to do an MR to maintain at least FO going into next year.

As an FO I enjoyed:
- A 25-30% upgrade rate, including a couple companion upgrades. Most upgrades were on the weekend and around the holidays and usually on shorter hops but were still nice.
- The free bag. If you have an DL branded AmEx, you then get two free bags. The free bag paid for the MR I did in 2009 to get to FO paid for itself within a few trips.
- Access to preferred seating (exit row) and free EC at T-24. I took very few flights where I wasn't in an exit row or EC or upgraded.
- Priority check-in line, which is a small but nice perk.
- Dedicated phone line
- IROPS rebooking priority. My Medallion status is the only reason I was #2 of 50 for three remaining seats and got home for Christmas one year after I missed my original flight due to a delay.