I’m using this with the Eve Weather device. In your home, you have to be pretty close to access the information—it works across about 1/2 to 2/3 of my house. However, you can access across the internet via an Apple TV. Weird that the Weather is “unreachable” in my house but accessible when far away!
Accessing info from Eve Weather can be very slow. Often takes 4+ seconds to respond to Siri (“What is the temperature on my patio?”). The graphs take 20-30 seconds to retrieve data and update. The faint blue line that indicates progress is very subtle (easy to miss) and takes many seconds before _anything_ appears. Why can’t my iOS device update by itself every few hours (even just when phone is connected to power)?
Another annoyance is the “…” icon that (is suppose to) lead to the detailed graphs. I have to tap repeatedly to get to those screens.
Also, Homekit is supposed to be about home _automation_. There is no apparent way that any action could be triggered in the house based on Eve Weather data. iOS 9 is supposed to offer more Homekit features so I’ll update this if/when things change.
On the plus side, the app works with Homekit-enabled accessories from other manufacturers.