Just found relevant thread on reddit: https://www.reddit.com/r/Bitcoin/comments/3mhe5p/case_wallet_teardown/.

"As we are using secure elements, we are bound by NDA to not reveal the chip's APIs (this is part of the current security by obscurity model of this kind of architecture). Therefore we cannot publish our source code, nor could you compile yourself anyway, by lack of tools.
The attestation being embedded in our firmware, it is therefore not open source either."

There will be no source code for this device, because of NDAs.
Requires a lot of trust in the unknowns (people and code).