@xigma technically true but not a widespread problem these days statistically. The blacklists cover a small usage percentage.

The fact that a browser supports WebGL tells you nothing about which devices support it.

It all depends on the GPU and its drivers, browsers have blacklists of GPUs, but even if your device is not blacklisted, it may simply screw up, especially on mobile.

If you rely on WebGL on mobile then I would feel insecure too, but progressive enhancement is a thing.

I got recently asked to do a project in WegGL and the target audience has the latest gadgets so it will fly on mobile as well. A transaction will cost around $50k so it's a safe assumption, but I'll do more research.