It looks like they're based on Hetzner. I would guess they are building on Hetzner's dedicated servers. Not that that's a bad thing, I'm a big fan of their dedicated servers.
Source: The IP listed in one of their examples is 2a01:4f8:a0:380b::1. If you lookup the ASN it points to Hetzner.
Source: The IP listed in one of their examples is 2a01:4f8:a0:380b::1. If you lookup the ASN it points to Hetzner.