Simple Device Viewer is a community developed SmartApp, it’s not 3rd party so all your settings are stored by SmartThings. I can’t see anything you’ve added to the SmartApp and I don’t even have a way of finding out the total number of installations.
If you enable the Dashboard you can view it from any computer, but no one else will know the url, unless you give it out. If you did accidentally give the url to someone, they’d only be able to see the screens that you can see and it doesn’t support cameras.
All the screens are also visible within the SmartApp so enabling oAuth and the dashboard is optional.