With WP Shifty it is safe to add any rule to a scenario, because you can see the results immediately in live preview, without affecting the live site.
In the live preview you can set the device to test multiple screen resolutions. Also you can set the user role, set custom headers, cookies or even post data.
WP Shifty provides live preview, so you can see your changes immediately. By default the preview will be reloaded if you make any change on the live tab. However if you would like to make multiple changes at once, you can disable the autorefresh.
If you make any changes on the Editor tab, the preview won’t refresh automatically, however you can refresh it manually.