I just bought a house that has two 2nd gen protects along with traditional style detectors, So far so good! No false positives so far. I reset both detectors and had them go through their self test when we moved in and they both report being fully operational.

Neither of the protects are near the kitchen or regular smoke producing spaces though. However They are near bathrooms. I hear steam can set these off pretty easily but I have not had that experience.

I might buy more protects to replace the other detectors but I want to wait a bit and see if nest comes out with any other products.