Michael,
I came from the other direction, had Visa, MC and Discover and then signed up for AX.
About the time I was getting my photo business going strong. Chase, Bank of America, Capital One and others would wait for big balance and then change the rate to the max. I was paying way more than minimum and way ahead of the due date.
I had a bank line of credit, so I paid all of them off and cancelled each one. When I paid and called to cancel they begged me to stay but I was looking forward to destroying the plastic those crooks issued.
The first month I had my AX card my wife and I vacationed in Switzerland. We visited Sinar Bron and I found out they would sell cameras and lenses direct since I was there in person. Prices were less than half what stores charged in the USA. I needed them for my photo studio and bought a lot.
Next my wife found an expensive watch (Rolex). Again, less than half what it sells for in USA. When we attempted to purchase AX ask to speak to me from NYC. They spent only a moment on the line and then approved the purchase.
My wife loved me for that and I loved AX for not cutting me off when I was so far from home. We sold her old watch for almost enough to pay for the new one, a super deal.
I had the old original green card. AX ask me to get the gold one later and I accepted. Since then they have ask about the Platinum and some others but I just keep using the one I have.
Two years ago I had cash for a down payment on my car and when the dealership ask if I wanted to use a credit card, to my surprise it was accepted by AX.
I don't know what the limit is but the only time they hassle me is when I buy something on line in Japan, Korea or Australia and they will (sometimes) hold approval until they can check with me to be sure someone has not stolen my card.
I bought a Herman Miller chair for my office and the people in Chicago sent a defect. Yes it was a bargain but no value as it was. I returned it and requested a refund and continued to ask about the refund every week for nearly a month. I finally called them and they said:
"Too bad, it's been over a month now and you have to pay 15% restock fee, regardless of the reason."
I called AX, they issued a refund and wrote them up for being the scum bags they were.
Repeat story with a couple of camera vendors in NYC that attempted the same. Collect the money, promise to ship the next day and two weeks later they are still giving excuses. One call to AX and credit before I hung up phone.
The time that happened with Visa the credit card company requested I work with the seller and write a letter to them and they would take it under advisement. (Are you kidding?)
When I was doing Southwest Airlines Vacations magazine I was traveling constantly. In California I hired a guy that worked as a grip with a movie company to ride with me, helping me find locations and protecting my gear when my eyes were elsewhere.
Each day he ask to be paid in cash since I was from out of town, The local AX office cashed my personal checks every day in LA for over a week, hundreds of dollars a day even though my bank did not even have a branch in that state.
There are other occasions and other things, AX travel checks, insurance for rented cars in Europe and USA and of course the points. I bought a LCD TV and Canon camera with points last year.
Reciprocating for my being treated fair is so important, I sometimes walk out of places that refuse my AX card, even if I have enough cash to pay and a Visa in my wallet.