I too find myself going down the time-nut rabbit hole. I want a perfect 10 Mhz reference, not necessarily a time of day clock.

I was tempted to go the Atomic Clock route, based on actual cesium oscillators, having found a cheapish ($999) used CSAC on ebay[1]. However, once I started digging into the data sheets[2], I found something unacceptable, Pin 1, labeled "Tune", an analog tuning input.

It was then that I learned that while the Cesium vapor cells were accurate, they aged, and drifted, unlike a properly degaussed and Zeeman harmonic calibrated Cesium Beam atomic clock, which is a primary standard.

Further demotivating was learning they have a 5-10 year service life. That's a lot of money to pay for what's essentially a better OXCO.

I'll stick with GPS disciplined oscillators for now.

[1] https://www.ebay.com/itm/327134074179

[2] https://www.mouser.com/datasheet/2/523/Microsemi_CSAC_Space_...