Please be careful to turn off the campaign the second your voucher runs out. Otherwise you get a nasty bill. You will not receive a notification that your voucher is used up. You have to keep an eye on it yourself. And don't try and set an end date. It doesn't work :(
I set an end date on mine, and Facebook have said in an email, yes, we can see you set an end date. But the add did not end and the first I knew about it was when they had taken the money for it from my paypal. TIt ran a week over the end date. Even the daily update emails stopped on the end date, but not the ad. Facebook are now ignoring me.