The weather adjustment features are OK but because they use limited historic data they are not perfect. The developers are working on ways to record more history to improve this.
I find the ET calculation better suited my weather than the Zimmerman, but I still need to tweak it as the seasons cycle.
Here in Australia’s east we’ve had a hot summer with no rain for months, the ET worked well cycling up to 200% and during a recent cold spell back down the 75%. We had some rain today (only a couple of millimetres) and the ET adjusted to 75%, with more rain forecast over the next 5 days, I’ve manually set a rain delay for three days.
It’s important to specify your local weather station correctly, I had to define mine a few times to get it to sit on my local airport weather station properly.