The main motivation to build vs use an existing solution was a solid backup/DR story and the desire to be able to write custom business logic which is enforced inside the HSM.

It’s things like controlling where funds can go, or requiring specific authorization based on amount being move around, etc.

Being able to leverage hardware we are already familiar with or which has various certifications (such as Fips) is a neat bonus.

If you look at the code, you’ll see that the funds flow from “anywhere -> hot -> cold -> warm -> anywhere”. This is the minimal setup and you can add more layers if needed.