No, running locally is pretty standard.

Also what's weird is that this project seems to be primarily written in javascript. I can't imagine that's a pleasant user experience for generating tool paths...

it's a combination of JS, WASM, and WebGPU. the JIT engines are so much faster than you would imagine, especially if you tune your code right. workers allow for parallel processing on all of your CPU cores. WebGPU, at least in Chrome, is kind of amazing.