CBP, being part of DHS, use field apps written specifically for iPads and iPhones. In addition, the contract vehicle specifies both iOS and Android devices, specifically iPhone 7 and Samsung 7.
In actuality, the number of Android users had dropped significantly to where DHS now has a higher ratio for IOS vs Android. CBP, due to its use of these proprietary apps written specifically for iOS, use mainly iOS.
DHS has public facing web apps that they develop to be compatible with both iOS and Android. However, most of the development is on Windows machines, iPads, and Macs. There are no Android tablets in development, only to test apps.
The reason I say this is because I work in IT in the federal government and I work closely in the deployment of apps to the field. In addition, because I manage inventory for the contract teams, I know the equipment we deploy.
There are components in DHS that have a 92% iOS use. I myself used a Samsung SGS 5 when we first went from BlackBerry to Android and iOS. I lasted less than a year. Good Technology did not play well with Samsung's flavor of Android. So I moved to an iPhone 6 which encountered no problems with Good and I just had an upgrade to iPhone 7. The DHS component agencies offer Samsung 7 on Verizon with a yearly upgrade cycle or an iPhone 7 on AT&T with an 18 month upgrade cycle. I prefer the slower upgrade cycle with the better interface with Good that I get in iOS. Android presence is minuscule.