I don't see the need for a 3rd party to interfere with the process. Google doesn't have the secure infrastructure setup like the credit card companies who have been doing it for eons. It may be that this is just an app that actually calls on the credit card network in the background, so Google isn't really providing anything but an interface on top of everything. I'm sure this is what's going on.
I would rather use a wallet app created by the credit card companies themselves. They are the masters in security, not Google.