From experience I can tell you that such a setup is very brittle and will fail the moment the one employee of that customer who knows about this is on vacation or working at a different place.
The only thing that works reliably is a proper VPN (configured for machine to machine access, not based on username/password which has the same brittleness issue) which these days is available at every customer's site.
I agree with the reliability issue, but I can't stop myself from mentioning that I had an autossh connection set up on systemd that worked for an impossible five years until our support contract expired.
The only thing that works reliably is a proper VPN (configured for machine to machine access, not based on username/password which has the same brittleness issue) which these days is available at every customer's site.