I added an Ecobee, to replace a Nest that lost WiFi functionality, back in the day when Ecobee had stopped giving out API keys and the recommended work around was to treat it as a Homekit Device. I see now that the direct Ecobee integration no longer requires an API key and can function with just an Ecobee account name and password.
Right now I have the thermostat and 3 remote sensors that work reasonably well. What would I gain in functionality by moving to the direct Ecobee integration? Is Homekit likely to be crippled or dropped following the lock-in/lock-out business strategy that seems to be the flavor of the month?
I look at this way, one less layer to have to troubleshoot if something breaks. So besides accessing via the ecobee portal, I use the ecobee integration for HA. Everything is on the wifi, no special protocols or other devices. Remember KISS (Keep it simple stupid)
They each have their strengths. The Homekit integration provides immediate state change notifications, while the direct integration is cloud-polling and only sees a state change about a minute after it happens. On the other hand, the direct integration exposes a few additional sensors, the most useful of which is “Equipment Running”, so you can see (for example) whether it’s operating in heat-pump or aux-heat mode.
I currently have both integrations running with no issues.