Yes but the Pi is calling home, so isn't that trading privacy for convenience? And I fail to understand how it's more secure than ssh + private key? There is still a connection outside.
Most of us on HN use our own VPNs, or have a dozen other ways to get at infrastructure from anywhere (and mosh, as others have suggested, is a better alternative for simple shell access over high-latency flaky connections)... but there are a _lot_ of people who don't want to (or couldn't figure out how to) maintain their own VPN. Or they want to deploy Pis at remote sites and each one has a weird and unique networking config, and they don't want to mess with Tailscale or the like.
It's a useful service, but it's not supposed to compete with homelabber setups, or enterprise solutions. At least I don't think so.