Ubiquiti has recently launched the UniFi Pro LTE over in the US, after it has been available in the EU and UK for a while. The main difference between pretty much all LTE hardware Ubiquiti offers, is that in the US the hardware is always locked to AT&T. The original UniFi LTE was so locked to AT&T that the price per GB was just way to expensive. While the UniFi LTE Pro is still locked to AT&T, at least now you can choose a SIM plan for you, which will likely be cheaper than going for the standard non-Pro version.
Price wise, it costs $279, can be powered by PoE and plugged into any port in the UniFi network. It does require a UniFi OS Console or a UniFi Gateway to form that VLAN tunnel it creates in the local network – however.
The EU version is much less restricted with support for LTE bands ‘LTE (1, 3, 7, 8, 20, 28), WCDMA (1, 8)’.
If you’re interested, you can find the US UniFi LTE Pro here.