Given their test and API documentation both refer to threads I'm guessing it must be using web workers. I might start offering it to desktop users, along with something like https://www.pollfish.com/, as ways to get rid of adverts on the site (I make sweet f.a. from ads, although I get pretty minimal levels of traffic, tbh - need to spend a lot of time on SEO, which is of course not the fun bit). I'm definitely steering clear of offering it on mobile though.