It's been available on iOS for a while, from today it's also on Android. Though not for my phone apparently.
It's not much more than the stuff on What's New Today on teh GW website, the occasional free wallpaper for devices, the list of new releases for GW, FW and BL when they get released, and it also includes licensed stuff like video games and so on. I think there are also occasionally free very short stories from Black Library.
It is up to date with official GW notifications, but usually like they are, a few days/weeks behind the rumour sites