I know very little about how it works. Can it be accessed without their software?
i don't think so, but they have a worse case scenario where you can sideload the app in case it gets taken down from app stores. there's no way for them to access your private keys like ledger though. https://bitkey.build/content/files/2023/11/Bitkey-Recovery-Features.pdf https://i.nostr.build/KPTjiLBXlBev4ikn.png
The Ledger private key storage is fully optional though, and you have a standard format seed phrase that can be moved anywhere. Sometimes it seems like in the quest to make everything simpler it gets paradoxically more complicated.