I found data usage quite surprising…
When playing Stadia on my Windows PC through the Chrome browser at 720p, Stadia used between 12 and 20Mbps. In contrast, a Netflix stream used about the same amount, but Netflix can buffer content to stop streaming constantly. Because Stadia is always pulling data and can’t buffer, it will use a lot more data.
You could technically use Stadia connected to a mobile hotspot, but I’d strongly advise against it if you have a limited data plan. Playing Stadia at 720p used about 7GB per hour.
Don’t expect to be playing Stadia at your local coffee shop without some comments or a lot of lag. I wonder if most of the cheap routers can sustain bandwidth like that anyway?