It strikes me that many of you are missing the point. This product seems to be aimed at people who make online transactions with companies they aren't so sure about. You know, places like Jimbo Billy Bob's Online Cyber Emporium, Zhang's Bargain Bin or Target.com. Not something you'd exactly be best served by driving to Walmart to buy a prepaid card every time you planned on making a transaction.
I have several credit cards but pretty much use one for all personal stuff and another for all business stuff. When I lost my personal card it was a non-trivial hassle to go through and fix all the billing info for recurring charges. This kind of service could protect somewhat against your information being stolen online and compromising cards you use for other things. In fact, we used to have a Discover credit card that let you generate card numbers with set limits just like this product for use in online transactions.
The intended users are not James Bond, Adam Kokesh or Theodore Kaczynski.
That said, you have to decide whether you trust this company enough to use it. If my credit card number gets out there I have to change my info for the people I do business with but chances are I won't owe anything out of pocket. If my bank account gets compromised through these people, I'm not guaranteed to get everything back.