Neat! If I'm reading the repository right, it looks like the avionics firmware ran on a TMS570 Cortex-R microcontroller made by TI: https://processors.wiki.ti.com/index.php/Category:TMS570 I'm pleasantly surprised to see that instead of a big Cortex-A or x86/64 chip. It's cool to read well-funded code for a small realtime SoC. you don't see them too often outside of things like memory controllers and safety-critical…
For low volume stuff, the chance of a detectable miscalculation occuring in the field is low, while the chance of a firmware bug causing a failure is high. Using a TMS570 for a hobby project would be a very poor choice. With a sufficiently high volume project, though, the development pain can be worth it.
The redundant cross checked CPU cores gives you piece of mind that the thing will self-diagnose a miscalculation and report it, rather than go off into the weeds. It enables you to responsibly design safety critical fault tolerant systems based on explicit handoff from one MCU to another. Without the cross checking, you can't trust a single MCU to act rationally; in designs like that, you typically need more than two MCUs with majority voting circuitry. So the TMS570 can help reduce total system complexity at the cost of lower level firmware pain.