Remember that if you're running a laptop equipped with Optimius technology, you will get the update feature installed automatically. You won't be able to deselect it during the installation process not uninstall via "Programs and feaures" applet in your Control Panel.
In this case you need to manually remove both user and related service or patch the script before in the setup file before installing.
NVIDIA claims they put every effort into securing this additional user as much as possible, but I wouldn't bother believing this. If anything happens to your system because of this additional user, you won't be able to recover anything from NVIDIA...
Since after manual removal of the additional user and service Windows works normally, I'd recommend getting rid of it asap.