I have a lot of observations to make about this product. I'll start with what I was faced with first.I live in a 2 story house, purchased last July. I live in South Carolina, where it's very humid and we rarely use our heating systems. The heater with air handler is located in the attic. The house was built in 2003. No one has ever replaced the contractor-installed Bryant brand heater. I've had these heaters before, and they are annoying. Whenever I replaced them in the past with a Trane furnace, my bill was cut in half and none of the ridiculous traits of the Bryant happened anymore. Those being the following: Cold spots in different places all over the house. A long ignite time, which means it's blowing cold air on you from the vents before it finally ignites. Too long to ignite. Uneven heating everywhere. Too hot upstairs, too cold downstairs. When the temps got below 35, it was unbearable downstairs unless I cranked it up to 70, which is a high temp for me on the thermostat in the winter.My AC condenser was replaced recently, so in the summer the air conditioner handled everything very well. It is a 4 ton unit and unrelated brand to the Bryant. (not a very good plan, but at least the AC works well). The AC has none of the issues that the furnace has. It works great.There's a problem, though. Because past owners pieced together a different AC system, the two systems are not as efficient as they could be. They also just can't put in a furnace and make it all work. Not the kind of efficiency furnace I've bought before.I just needed a furnace, but not an AC unit. So, I set out to talk to all these Trane installers. I love the two stage AC units from Trane because they only go into the higher mode when they really have to. The answer I got?"You can't change out only one unit. It has to be both." (something I knew from previous houses, anyway).Installer: "That's going to cost you $13,000.00"Me: "Gulp. I know that they really need to both be married up, in order for them to work well."Installer: "No other way, with this pieced together system you have right now."The problem with this? I didn't have the cash. Lowes would only loan me $6,000 at no interest. I always went for no interest loans in the past. Wells Fargo would only give me 5,700.00 but I could not combine both of these financing options. No one would loan me (or anyone else) that much money. I could've gone with a personal line of credit at my bank, but it was 10 - 12 %. Banks are a lot tighter with home improvement loans these days, since GE sold its finance division to a company called MySynchrony. GE gave me 15,000.00 no interest for the first year once. Not anymore.So, I set out to get 4 more quotes. Same answer from all of them. So, I was stuck with running downstairs to turn the heat down at night because I felt like I was going to suffocate upstairs, then running downstairs in the morning to turn it up to get it warmer down there.Then I remembered the Nest. It's expensive, yes. But .....it is better to at least try to spend $248.00 instead of 13 grand.(All the quotes I got were pretty much the same.)At the very least, I could incorporate it into a new system in the future.Install: Easiest install of any thermostat I've ever performed. I've always done my own installs because I liked Honeywell for many years, but there are no screws or difficult, cramped holes to put the wires into. You don't have to read a book to figure out which wires to use and guess what kind of system you have. It already knew, once I installed it.It's connected to the Internet through your WIFI. If I'm upstairs with the heat on and it gets too hot up there, I just pick up my iPhone, go to the app and adjust it. If I want to go downstairs in the morning and know I have it set to 65 down there, I just heat it up a bit on my iPhone before I get out of bed.It learns. I'm not quite sure what it will learn from me, because I'm retired and usually keep things about the same. But, the programming was extremely easy, both on the unit and on the iPhone app. Change it anytime I want.I was at the doctor yesterday. Realized that just my dogs were at home and I had started the AC this past weekend. (You can switch between heat and air any time you want on the iPhone or iPad app...awesome. ) So, I just turned up the AC to a warmer temp because my dogs aren't too crazy about it being really cold. Before I got home, I set it back to 70 for AC, where I like it. I was bed-ridden after some spinal injections this past weekend. I was praising this thing for making my life comfortable while I recuperated upstairs. Before, it would've been absolute agony to go downstairs all the time because South Carolina is in Spring already. You never know what the day will be like. I just changed it when I needed to on my iPhone.The WIFI was easy to connect, once I realized that you turn the unit itself with a rotating dial either left or right, then press on the choice you want. No annoying methods to type in your password like it is on a Bluray player to login to an app like Netflix. Those are a pain.The screen is motion-sensing on the unit, so you just have to walk by or wave your hand to see its settings. It seems to also get my systems to the correct temperature WAY faster than my Honeywell thermostat did. Seconds vs minutes.Now: I've saved $13 Grand. For now. It's made my furnace manageable in a two story house. I can save up the cash for a new system. It has a mode called Airwave that is supposed to save you on AC costs. I'll know in July and August if that works well.I believe it's going to save me a lot of money and allow me the time to save up for the new system that I really want. I will have my installers just leave the Nest there. It's an incredible product. I've not found one bug with it yet. It's only been about 5 days, but it is already telling me it is learning.Love this product. So glad I bought it. It's the best piece of technology I've bought so far, besides the iPad Pro.Thank you Nest. You saved me a lot of money for now.A few months later:This product is already saving me a lot of money. It's already saved me $40.00 this month on electric. One thing I wanted to mention was someone was complaining about the way it displays the temperature. I think that it is just a matter of getting used to it because there is a rare occasion that the large number in the middle and the smaller number are not the same. What I've noticed is it gets my system up to the correct temperature way faster, and so I'm really not so concerned with the smaller number anymore.I also saw that someone was complaining about the Away function if you don't walk in front of it often and waking up to a cold house. I'm retired, so I don't really need a regular Away function. I go out at really different times, so I went into the settings on the App and turned that off. Problem solved.I love that my air conditioner doesn't run as much as it used to, and I noticed I don't have as much cold air coming out of the vents when the heater is working.I also get an email of my usage each month from Nest. (see image) The leafs mean you've set your temp to an energy-saving setting and will also show up on the dial.And It's still saved me 13 grand. Win win for me.