Steinberg will of course not comment on this, but it’s “ok” to use it if you own a legal Cubase license, and you don’t mind the potential security risks and your Internet Service Provider knowing that you downloaded stuff from a warez site.
Quadrafuzz v1 sounds pretty dated though. I would recommend looking into alternatives. Most of them wont sound as rough and loud, but they’ll likely improve the sound of your mixes in the long run.