Are Full Screen Popups Ideal for Desktop or Mobile?

Desktop. A full screen popup has room to breathe on a big monitor, but on a phone it hides everything the visitor came to read. Google's guidance on intrusive interstitials says not to obscure the entire page, and suggests small banners instead.

1. On your Capture's Setup tab, choose Takeover as the type. That's our full screen Capture.
2. Open the Targeting tab, click Add New Rule, choose Browser, then Device.
3. Tick Desktop only.

Create a second Capture with the same offer as a Bar or Floating type, and tick Mobile in its Device rule. Phone visitors still see your giveaway without losing the page.

Tablets sit in between. Tick Tablet on whichever version looks better when you test it on a real device.

The Browser rules docs cover Device, Screen Width and the other options.