The core integration works fine.
With a couple of caveats:
-
If you create calculated sensors in the IoTaWatt (called “outputs”) they will not show up as entities on the IoTaWatt device page. They are still available as entities in home assistant though. You can see them in Developer Tools → States or the Devices & Services Entities tab. The reason for this is that the entities do not have a unique id. This does not stop you using them in the energy dashboard or anywhere else in Home Assistant (e.g. automations). There is a 3rd part integration that does list the outputs on the IoTaWatt device page but it has other issues - like not resetting exactly at midnight which messes up the energy dashboard. I found no good way to fix this. So just use the core integration and know to find your outputs in the entities list.
-
If you have a power outage the energy sensors will glitch and cause massive energy spikes in the Energy dashboard. You can not fix this with template sensors. The only solution is to use a small DC UPS so that the IoTaWatt is always powered. e.g. this: https://www.wagneronline.com.au/5v-9v-12v-38-5wh-dc-in-line-mini-ups/power-12vdc/power-lighting/ups5912-101087/1007502/pd/ will keep the IoTaWatt powered for more than a day without mains power. If you have a power outage longer than this you have bigger problems to worry about.
There is an ESP32 IoTaWatt in development. Good progress is being made but there is no release date information or even a guarantee this will ever become a commercial product. You can read about it here: ESP32 version 0.3 - Bob's Blog - IoTaWatt User Community
Since switching to the core integration and using the DC UPS I have been very happy with my IoTaWatt. It agrees with my billing information to better than 2%.