Good point. It opens a SSH tunnel from Pinggy server to your localhost, such that the pinggy server can connect to only the port of your localhost that you specify in the command. The ssh port forwarding command is a standard one and your ssh client ensures that the access is restricted to the port you are specifically exposing.

In other words, you are trusting your own system and your ssh client installation for security, which is more trustworthy than a random executable app downloaded from the internet.

We will include an explanation in the next version of our landing page. Appreciate your feedback!

On the bright side, at least the part you're running is off-the-shelf parts whose implications you can more or less figure out by consulting the man page. Other services in this space are trying to convince you to run their own binary blobs.