I travel frequently, and on international flights I've always flown economy, as the price of a business class ticket is often triple that of economy.

However, after looking at the chart for upgrades:

https://www.aa.com/i18n/AAdvantage/r...rade-chart.jsp

I noticed that it would only cost me $350 plus 25,000 miles to upgrade from a North America flight to Tokyo. If a mile is 2 cents, then that is about $850 total.

This is much cheaper than buying a business class ticket outright, which is usually about $3,000 more.

Seems like a great deal. Is there a catch or caveat?