5 stars: I first had the same problems as everybody else. Connectivity, charging, etc. Ember sent me a new base for the mug, which was the problem. Since then, no problems, it works great. You may occasionally have to stop the app manually and restart it, but that's minor. And their support is very helpful.
4 stars: After the first day, which seems to consist of struggling to get it connected after updating the firmware, it works pretty reliably, and I'm very happy with it. Onboarding is always a struggle with anything Bluetooth related (especially on Android) so I won't whine too much.
3 stars: Originally, this app performed horribly. I couldn't install firmware updates and constantly lost my connection with the mug. Things have changed. As of a couple of updates ago, with nothing changing on my phone that I'm aware of, the mug updates flawlessly and my connection is stable. Lovely and much needed improvement. Thank you Ember for preserving though it took way too long. The UI/UX could use improvement but I'm much happier now.
2 stars: Very poor quality software, I understand that the mug can function without connecting to the app but it's still really annoying that the only way to connect the mug is to remove it from the app and start the pairing from scratch each time. (note that this has been the situation from the start, with multiple versions of the software, two different mugs and half a dozen phones)
2 stars: Stupid application design. The app asks you...