It's safe. It's just trying to tell you that you shouldn't run the server code on a computer connected directly to the Internet. No one in their right mind would expose their computer that way and if you're using a Roku you must already have a router that acts as a firewall. Your Roku and your computer should both show that they are using an IP address of the form 192.168.x.x or 10.x.x.x. It they are (and they almost certainly are) then they are behind a firewall and there's no security issue.