If one is selling lots of devices with web interface, it may not make sense to use Letsencrypt service built-in because it requires generating unique domain names which are not user-friendly?
Are we want routers that open its admin page to internet?
It depends! There are two basic aporoaches in common use:
- generate a unique DNS name and make it publicly resolvable, then have the devices generate certificates for those names, or
- have a cloud service with a single name that communicates with the devices.