Thoughts:
1. New design just came out. I you are going to do this make sure you get the latest version.
2. Intuitive--easy to use.
3. Have a bunch of Nest Protects--house knows when folks are home and when they are not.
4. Have seen some savings--however, just picked up two foster kids which means more people home during more days which translates into increased usage. This skews the data.

Worth it? I think so. Plenty of other products that will do the same tricks when considered as a standalone product. However, when paired with the smoke alarms / cameras / IF then it opens up a nice world of possibilities.

Would I buy it again? Yup.