Did clicking on the Rent my PC tab really try to benchmark my GPU through my browser, or did I accidentally click another button on that page inadvertently that triggered that?

If the former, that's a terrible idea. If the latter, that button really needs a confirmation and explanation of what's about to happen.

I'm viewing on an Intel Mac and it hung my entire computer for like 15 seconds. I didn't even connect that it was related to viewing your site until I got the error at the end and everything unfroze.