The first new feature we got on BOTH models was synced alarms! Why? It was already most hated feature on a stand-alone setup.
Also, their communication system between the models is a VERY noisy ad hoc wiresless audio mesh network.
(I have to admit it works better than our Wifi across the apartment – but I guess it’s because there’s no legal TX Watt limits!)
No user documentation was provided except for incorrect sharing of information from family.
Mine was frustrating at times but looking back it was well worth the price paid