I couldn't find any mention on the website -- does it support one time numbers for online transactions? If not, I'd be very reluctant to use it. One breach and your bitcoin account is gone.
Nerver used bitcoin, but cannot you simply create another bitcoin account for petty cash VISA transactions and transfer funds when need be?
Many bitcoin users prefer to generate a new incoming address for each transaction to improve privacy (Bitcoin is "anonymous" only insofar as your legal name is usually not directly attached to the transaction; in most other ways, it's more traceable than the alternatives).