They are still new in the US so there aren't many options out there but from what I read, they work similar to a debit card. I guess you will be tied in with them through your bank so if you fail to pay them back, they can take the money. I feel like this is a bit fishy and I don't trust them. I need a contract to read over.
I have never looked into one myself but I have heard of them. They seem to come with their own risks you have to be aware of. Just like going with a contract free cell phone carrier.
I have one with Capital One. You can read about them here: https://www.capitalone.com/learn-grow/privacy-security/contactless-credit-cards/
I think some of them out there are not quite the same as this one. I got this more for security and controlled banking than anything.
I have never even heard of these. I guess they aren't common where I live. No banks or anything around here offer them but I can see why they can be beneficial for some people.
A friend of mine got one of these. I personally don't see the point in them. It is like using a bank card with extra steps. I can't think of any scenario where this is better for someone.