Earlier quoted context omitted.
No, it expires after they view it.
Yes, this is a nice solution, but email security services do click on links before delivering to the client's email inbox. As such, you may need to set the link expiry click number to greater than 1. And then you lose the security due to being ephemeral. Of course, you can log the IP addresses of the clickers, but still you have the leak.
Like I said, I've used a similar service that only allows you to view the secret once and I've used it dozens of times with no problems.