Is anyone actually using this (and other open source solutions that do similar things) for anything?

The cloud providers offer "serverless" billing for AWS Lambda/GCP Functions/Azure Functions in the sense that you pay just for the compute time and don't manage the underlying infrastructure.

Outside of vendor lock in, what advantage does running a service like this really offer? To make a system like this usable you'll probably need at least a couple of boxes available 24/7