This website is running at >10 FPS at 100% GPU usage
Developers especially with tech demos like this, use the latest tech to develop and don't care about supporting older devices. This attitude can sometimes bleed over into their work where they should care for users using older machines, but its expected for a look-at-the-shiny demonstration to other techies using top of the range hardware.
( I am seeing the same laggy effects on an older linux + firefox laptop with integrated graphics, unsurprisingly )