I have a Nexia Z-wave stat on my heat pump here at home. When I set it up, appeared to be in constant communications with Nexia sending status information. The cellular service I have has no unlimited data plan. With the maximum of 20GB/mo. data plan I have that's shared among 2-iPhones, 1-iPad, 1-Android and 3 Windows computers, it's a challenge to stay within the data limit. Therefore, I don't do YouTube, streaming, or any other data intensive activities, I don't believe the Nexia thermostat is a big data user, but it's a constant data user; which could add up. So, I leave it's Wi-Fi off until I can run some tests to determine how much data it actually uses.
The current Nexia replaced two older Nexia thermostats that failed in the four years since we had the heat pump installed- the first was replaced under warranty, the second was not. Due to the poor reliability demonstrated the first two thermostats, I refused pay for another one of the same questionable reliability and spent $$$ to have it replaced with a newer, and hopefully, more reliable model Nexia thermostat. It's been in service only since December 2018, so it's yet to be proven whether it will outlive its previous two thermostat "cousins".