Then don't.

They said "if you have a free computer", meaning one that isn't used.

Also, you can wipe the computer and re-install the OS afterwards.

Finally, whenever you install any kind of software, you are giving someone remote access to your hardware in one form or another.

You can just set it up in vm with passthrough for that card by now I believe. All the cards he's looking for should work fine that way I believe.

You can also pass the VM's network through a VPN.