Re: Circle.com - Anyone out there using it? What are your experiences so far?
Looks like its for US customers only 
Some Australians at least are having success with linking Visa *debit* cards (but I could not link my Mastercard *debit* card).
Too risky to link my cards with this kind of stuff.
What are you worried about? You are covered on the credit card side by their consumer protection anyways.