Bought one of these for the current Mrs. Undergroove and although it's specced amazingly, it's driving her (and, by extension, me) up the wall...
As she had a Nexus 5 previously, I've set Google Now launcher as the default, as well as dropping to stock Google apps where available, so she's familiar with the way it all works.
Her niggles seem to centre around location and WiFi issues, such as dropping the home WiFi connection, Smart Lock not always working in the house, as well as the odd niggle with Bluetooth in the car.
I'd add that when I used the same physical phone for a few days I had none of the issues she had and, to be honest, had I not picked up a Nexus 6P myself, I'd be getting one of these bad boys.
Can't for the life of me figure out what she's doing that makes the phone misbehave in the way it is, and from reported issues I've seen, although the odd symptom matches her experience, there's nothing I can find to suggest it's anything other than a problem between chair and touchscreen... also pretty much ruled out any whacky apps shes installed and had her running it with nothing other than factory apps too.
All a bit vague and wishy washy, but other than swapping out the current Mrs. Undergroove for a newer and less temperamental model I'm a bit stumped really. Loath to change the phone too, as I don't think there's anything wrong with that!
Suggestions on a postcard please to the usual address c/o the Blue Peter garden etc.