It seems to be pretty reliable (and good audio quality!) from my tests. I've only got two issues with it:
1) It can't be set as the default dialer yet.
2) Incoming calls ring both Hangouts and the standard Phone app. It seems to be a bit of a race to see which one rings first. Back in the days when I tinkered with various VoIP options, I used some Tasker hackery to avoid this conflict by way of disabling the cellular radio while connected to Wi-Fi. I hope that Google can work up a more elegant solution. Automatically ringing *only* Hangouts while I'm signed in and connected would be pretty sweet.
1) It can't be set as the default dialer yet.
2) Incoming calls ring both Hangouts and the standard Phone app. It seems to be a bit of a race to see which one rings first. Back in the days when I tinkered with various VoIP options, I used some Tasker hackery to avoid this conflict by way of disabling the cellular radio while connected to Wi-Fi. I hope that Google can work up a more elegant solution. Automatically ringing *only* Hangouts while I'm signed in and connected would be pretty sweet.

