I opted for the E version of the thermostat since it was less expensive than the full version, but I do not believe I am missing anything important. The E does not detect motion to know if anyone is home, though thermostats are not always located in areas that could detect motion sufficiently to be useful. (mine is in the hallway, and would never see me during the day) The plastic body does not feel any cheaper than my old thermostat, so having a plastic version is also not a huge loss. Overall, the body feels solid, and the menu system is easy to use. The smoky numbers used for the E that only display when I am in the vicinity of the thermostat is better looking to me than bright numbers. The numbers are visible from several feet away, so I just need to move in front of it to see the temperature setting.
The Nest app is easy to use, and the ability to schedule temperatures for the system that change throughout the day is great. I have my home warm up in the morning to wake me up, and cool down at night to facilitate sleep. Each day can be individually scheduled, and the schedule can be set-up/modified on the phone or though a computer. The home-away is nice, though not always reliable since it requires the phone and the app to communicate properly. There have been many days when it did not register me leaving, and it takes time for it to figure out I am home. I found using Google Home routines for work days to change the system to Eco while I am at work more useful than the home-away assist. Being able to check to see if my kids have adjusted the thermostat when I am away from home is also nice, as is adjusting the thermostat through my phone or Google Home without having to get up.
Finally, setup is relatively easy if you know some basic wiring. As recommended, take a picture of the old thermostat wiring before pulling wires off. Also, add the labels to the wires as they are being removed. The second one is always easier to install than the first one. And, the face place provided with the Nest will help hide the missing paint behind the old thermostat since the sizes will be different.