Cheap second hand rubidium frequency standards may be worthwhile, unlike new rubidium oscillators, which are not that good in comparison with good OCXOs to make their much higher price acceptable.
Traditional rubidium frequency standards still have an aging rate that is high enough to be non-negligible. While from the datasheet of a rubidium oscillator it appears that it is better than an OCXO, that can be misleading, because many OCXOs have very predictable aging drifts. If you compensate the aging in software, you may reach a similar performance to a rubidium oscillator.
In recent years there have been invented several new kinds of rubidium frequency standards, with much better performances than the traditional models. However these are either not available yet as commercial products or they may have a single provider which demands a steep price.
Traditional rubidium frequency standards still have an aging rate that is high enough to be non-negligible. While from the datasheet of a rubidium oscillator it appears that it is better than an OCXO, that can be misleading, because many OCXOs have very predictable aging drifts. If you compensate the aging in software, you may reach a similar performance to a rubidium oscillator.
In recent years there have been invented several new kinds of rubidium frequency standards, with much better performances than the traditional models. However these are either not available yet as commercial products or they may have a single provider which demands a steep price.