Good. That also tells you that your server probably needs some DOS mitigation. Because if their service almost takes it down, so can a trivial nmap sweep.
Yes, my site does - but that's not the point - it's a text field on a website anyone can use to hit any site without effort.
It's also supposed to be a helpful service, which generally implies it's not gonna behave in a way some would consider to be malicious, but it has no rate limits. If I saw that hit my logs i'd consider it to be an attack, not a friendly vulnerability scan.
It's not super fast, but it's not really slow. A single web server doing 50 req/s, and they pushed that up to 100 req/s. The limit is somewhere around 75.