[sourcefrog]

They will work over the internet. You should use SSH or a VPN like Tailscale because the native protocol is not encrypted.

Bandwidth and latency effects will have some effect on how well it will scale, but on a reasonably high latency and low RTT connection it's probably still faster than purely local compilation. Sending work over the network takes time but not much CPU, so the local CPU is freed up to do other work.