We track pressure and temperature in the duct via an embedded pressure and temperature sensor in every Smart Vent. If the pressure in the duct is between .5 and 1.4 iwc, the vents will automatically open enough to reduce the pressure. We also recommend leaving dumb vents open while Smart Vents are installed.
You don’t have to replace the thermostats. Smart Vents work great on their own with standard thermostats. But if you to want to connect your thermostat to your Smart Vents, you can do so with Nest, thermostats on SmartThings (Yves Racine has built a Smart App that allows the Smart Vent to work with Ecobee), or a thermostat on Lowe’s Iris. We’re an official Works With Nest company and are also working on native Ecobee support.
You can use a separate remote temperature sensor on SmartThings to augment the abilities of the Smart Vent, but you really don’t need to. We’ve been working hard on a controls algorithm that allows us to determine room temperature from within the duct, without needing a separate sensor.
Regarding your last point: that would be ideal for sure. It’s the long term idea behind Works With Nest. Nest thermostats support wifi, 802.15.4 (Zigbee), and Bluetooth low energy, so they could be a hub in the near future.