it's basically a 2 of 3 signature device: hardware, phone, cloud. 

if you lose your phone and device, you set up a list of trusted contacts that can help you recover your cloud backup with a new hardware

i've been playing around with it, seems cool, even though I'm not still 100% sure what happens if bitkey servers ever go down or the company disappears 

https://support.bitkey.world/hc/en-us/articles/24493244382484-I-lost-both-my-phone-AND-my-Bitkey-hardware-device-What-should-I-do