The discover ones weren't time/amount limited so they didn't solve the recurring transaction problem as long as it was the same merchant making the charge. The

The discover ones weren't time/amount limited so they didn't solve the recurring transaction problem as long as it was the same merchant making the charge. The security with the discover ones were also their largest problem. The number was basically locked to the merchant account/service provider where the charge was initially made. So places like amazon that seem to use multiple CC processors (or just hand of the numbers to 3rd parties, not sure what they are actually doing) wouldn't work with them. My MC though has a similar service where I can select the expiration and max amount that can be charged. I've used them to buy services I didn't want to bother canceling in the past. Although again, they sometimes don't seem to work (probably because the numbers are listed as prepaid).