I've bought three of these (also one 3rd gen metal thermostat) with the free google mini chalk devices. It was an easy setup, just use the provided stickers to label each of your wires. You should shut the power to your unit so you don't touch the small thermostat wires together during removal of your old stat and when installing the Nest stat, because you can short out your HVAC control board. I didn't shut off the power since I do this for a living and was careful with the wires.
You can use the plastic rectangle base plate or just leave the circle thermostat by itself on the wall.
Setup was easy, just follow the step-step guidelines on the thermostat when you power it up. After a few days I was able to see my power consumption and temp changes on the history trends through the phone app/web app. It can control heat pumps and you can choose when to let the Nest stat use the emergency electrical heating strips also, it's pretty configurable.
It has a motion sensor that will sense when someone is close by (it picked me up in an open area at around 20ft just like my newer model 3rd gen metal thermostat for $249) and then the display lights up. I use my phone app mostly which is awesome especially if you are in bed or if you are at work and you forgot to lower/raise the stat before you left home or your wife texts you to change the temp downstairs because she is too lazy to go downstairs (she doesn't have the Nest app on her phone yet.) The stat learns your behavior pretty good, I don't use the economy away mode setting since I have several family members that are home when I'm also at work. The away mode eventually knows when you leave for work and automatically puts your stat in economy mode and then 15 minutes before you come home from work it will bring up the stat to the temp you like). The stat has a humidity sensor also to give you the humidity. It doesn't display the weather information for your area like the newer model third genertaion metal looking Thermostat (I have one of these also, both the 3rd gen and E stat have the same hardware and software, just the 3rd gen shows weather info and looks nicer, but I don't think the extra $80 for the 3rd gen is worth it unless you want to splurge).
CONS: It didn't come with any sheetwall anchors for the provided screws. I would recommend getting them, the holes are not like the older thermostat hole patterns, I've had to make new holes for all three of my stats, it wasn't a major problem. It does come with a built in bubble leveler to straighten the stat, which I didn't think it really needed, the screw holes are elongated so you can tweak it after you screw it onto the wall (there are two screws for the base plate and another two screws for the thermostat or you if don't use the base plate it's just the two screws.