I suppose buying a $130 box that no longer works AT ALL because the cloud backing it and providing all of the functionality is gone isn't a reason to want longevity? It would be like buying a mobile phone locked to one network that fails. If Google were giving this away for free and charging monthly I'd agree. Welp service down, no more $10 a month from me, moving along.

The $130 box gives you a controller and a Chromecast Ultra. You can use both of the outside of Stadia.

They are also optional: you'll be able to play on Stadia without the controller and without the Chromecast (e.g. on a computer with mouse and keyboard).

What else can you use the controller for? Is it a standard HID?

I don't have prior experience with controllers, and I don't know what is standard. But I can play my steam games with the Stadia controller and use it with https://html5gamepad.com/ (on Windows).

You "buy" games for Stadia, you don't rent them.