Aprilaire had some hiccups out of the gate with the 8800 communicating series, and the fix was the exact same thing listed here... dedicated power.

They are extremely reliable now.

Dedicated power should be considered a best practice on any 'smart' thermostat.

The #1 drawback to NEST vs Aprilaire is that the NEST is not compatible with as many advanced heating and cooling systems.

If your clients home (or your own home) has a sophisticated HVAC system, Aprilaire may be a better choice. For the more straightforward HVAC systems, the online and iOS/Android UI from NEST is pretty compelling.