[fariszr]

It's a compromise.It's not as secure as using a VPN, but it's way more convenient, since only one device has to have a knocker client on it without needing any sort of VPN.

The likelihood of someone is on the same network as you noticing your servic, try to hack it, before the TTL expires again is IMO quite low.

This is without taking into account that the services themselves have their own security and login processes, getting a port open doesn't mean the service is hacked.