Garnet vs. rolling your own
Both keep your data in your building. The difference is who does the work, and who you call when it breaks.
Roll your own
The open-source pieces are real and good. Assembling them, hardening the boundary, and keeping it all running is the job.
If you have ruled out sending confidential work to the cloud, you have two honest options: commission a Garnet build, or roll your own private AI from open-source parts. Both keep your data on hardware in your building. The real difference is the engineering time, the security hardening of the offline boundary, the hardware you must size and source, and who you call when it stops answering. A Garnet build hands you a finished, hardened system that Garnet designs, installs, and stands behind; family-office, private, and enterprise builds are scoped on request. Rolling your own means you own all of it, and all of the work.