I saw your comments and was wondering why you wouldn't trust the service? It seems that the data is encrypted when sent between devices. What is preventing you from using this for passwords ?
My guess is that it is safe and the owner is not eavesdropping the conversation. But it is impossible to be 100% sure. (Just call me paranoid if you wish.)
I tried a few times with not secret data and it works.
I tried a few times with not secret data and it works.