Well worth it, if you dont want to give bank details to Blizzard. I use these to play wow and never had any issues.
But its worth mentioning that you can actually buy pay-time, from the Blizzard online store like you would a game or a dvd. You can chooe 30, 90 or 180 days worth of online gaming.
It works exactly the same way as the card does except you are sent the number (which is normally on the back of the pre-pay card to scratch to reveal) in an email from Blizzard.
It actually works out cheaper to buy 180 days online from Blizzard, then to buy 60 Days using a card like above.
I guess its also easier on the environment and you, because you dont have a CD case to throw away. I have a few collecting up now from all the pre-payy cards ive bought in the passt.
But either way, its the same process.
You can just choose to pay for 60 days using a card like this, or 30,90,180 days on the Blizzard website. Neither requires you to give any bank details, except obvious card details.
But its the players choice.