They seem relatively cheap for what they are. I know there are cheaper displays out there but in terms of development time they seem ideal. I have only done a couple of projects with graphic displays but I found they are a real pain. You tend to end up with a load of librarys font files etc and spend a lot of time with trial and error trying to get the display looking right.
With these displays you design the GUI with a wysiwyg editor (Windows Only). All the images fonts etc are stored in the screens memory so your uP has only got to do its read its sensors and send it to the data to the display.
I was thinking of combining this with an esp8266 in transparent bridge mode to give me access to my energy monitor data.
The data is collected and processed by a Maple mini and I just send text strings to the ESP over serial with the data in it.
In my Energy monitor project I used a raspberry pi driving a samsung picture frame as an output device. Eventually I got fed up with the PI messing up the SD cards after the 5th reload I gave it up.
what does you energy monitor do?
Mine is just uses the Open Energy Monitor library, and senses 2 analog channels (Voltage sense and current sense), which gives me the voltage, current,real power, apparent power and power factor (thanks to emonlib)
The main thing I needed was that the direction of power flow , as most commercial clip on power monitors don’t show direction of flow (which is very important for making the most of solar PV systems).
Also the commercial clamp on monitors seem very inaccurate.
I’ve not really tested the linearity of my system, apart from at a few fixed points, e.g. 0W, 1kW, 2Kw and it seems OK, but of course it could be wrong at 250W or 500W, in which case I’ll need to build a calibration table into the firmware.
what does you energy monitor do?
Yes. I know that if you can monitor 2 clamps and know that one only consumes power and the line from the solar PV that can only supply power, you can determine net power flow in or out of the house.
But in some installations its hard to access all of those points, and if I measure voltage as well as current I get a more accurate result, as my voltage supply varies considerably from hour to hour, which can give me a 10% error in voltage.
So as I have to measure voltage, I may as well just measure current in one place and let eMon lib do all the work 
My setup was more to find out how much I was exporting which turned out to be about 68% of what I generated. Also I wanted to find out my background power which turned out to be around 300w. I looked at solutions for power factor etc but the information would not be of any benefit to me. The cost of a accurate voltage transformer would not give me any useful info, not that others could not use it. I am contemplating getting an air source heat pump to heat water with my excess power. It draws only 900w so most days I will have enough excess power to run it for 1 hour a day.
I run a heat pump, well I run a reverse cycle air conditioner which has a Economy mode – however I’m not sure what power economy takes, but I think its around the 1kW mark.
But its difficult for me to control, unless I rig out some sort of IR control
I can’t find the exact model but the one I was looking at was 900W IN and approximately 3KW out depending on the air temp. My plan is to test the output water temp if it drops below 40C a bypass valve will mix the water with cold and feed 20C water to my combi boiler. My combi boiler does not accept pre heated water but 20C water should not be a problem. Also it will increase my water flow in the winter. Heating water from 20c to 40c is much easier than from 5C in the winter.
Ah. OK. I stayed at a small hotel that seemed to have switched to using this method to heat water. Its supposed to be more efficient than normal resistive heating. But of course the initial costs are higher, and its harder to control
I’m about to start to design an ESP8266 based power dimmer controller for a normal resistive based water heater.
I have ordered 2 sizes of them just after seeing on Indiegogo campaign; 2.4′ being the smallest of the family and 4.3′ one with good looking size. In general they are GREAT. Like Pixy camera module, Nextion is what people need for neat projects. The ideas are same; putting a microcontroller on same PCB with a sensor or a module, writing every related stuff in it, leaving some connection pins like the uart, spi or i2c. I have a collection list of Sparkfun products created with same concept : Sparkfun Wish List
Chinese friends surprisingly applied it on Nextion almost perfectly! 
What differs from common LCDs in the market, there is a STM32F030C8 chip in the back, which is fast enough to drive the LCD smoothly. Before thay arrived, I always thought that the chip must be STM32F103CB since it is very commonly used in many products (with naming as Maple) like Multicopter boards(or like those FlyMaple , DreamerMaple , Particle Photon) Embedding STM32F103CB on LCD modules was what I have been dreaming for some years!!! You can’t imagine how I felt broken when saw the Nextion 
Then I tought, I must act quickly when I have an idea In my current project, I am driving 1.44′ lcd (smaller than the Nextion boards).
Pluses and Minuses
+ Comes in very different sizes
+ Code uploading over serial port easily
+ Enough fast for many projects
+ Great memory and direct media transfer (without need of using SD card!)
+ Nice touch interface by a dedicated chip for touch input
+ The editor has Emulator, media convertor and direct uploading to Nextion
– Arduino library uses Serial to debug and Serial2 for LCD!
– The editor consists bugs and deficiencies for preparing nice GUIs (did I mention the poor English translations?)
– Code uploading and communication ports are same (you should plug out it to update the lcd content)
– Choosing different fonts it’s not working (will be solved probably).
Projects
I wanted to use 4.3′ Nextion for my energy monitoring system too! I have purchased LCD and Itead RBoard. However, the Arduino library was poor for Atmega328 users. Serial is devoted to debugging, and SoftwareSerial isn’t used for LCD! Multi hardware Serial enabled boards (Arduino Mega, Due and STM32) can be used with the library easily. However, it was not that hard for me to integrate SoftwareSerial and connect LCD on analog pins of RBoard (since there is no any digital pins). I have two of the AC current sensors and the data is shown on the LCD on gauges. (I am planning to mention about this later under a new topic with photos)
With smaller 2.4′ LCD, I am planning to make a remote controller module for another project but again with RBoard. Via Bluetooth or NRF24L01 module, I want to control Relays. Of course using NRF with Nextion requires a small microcontroller(like Atmega 328)
The Nextion Editor
The Editor, on the contrary, is poor since doesn’t allow you to control everything. The GUI is also very amateurish 
Gauge is, for example, very simple looking, just a line. However they are improving everything and I am expecting a better one in near future. For the curious ones, there is no way of creating primitive drawings, playing a video, multi touch options, transparent images or sliding pages.
Possibilities
One of the idea I came up is plugging a bluetooth module (like HC-05) and remoting LCD wirelesly! Another suggestion is finding a way to hack STM32 chip and find a way to write code directly! 
It would be good for professional works like a drawing pad with primitives. Another example is creating access to SD card and making a photo frame 
Ive been trying to use the arduino library but it uses avr code like itoa and utoa… not really sure what to do about that.
Been reading more on it, dont need the library, it really is some simple serial strings…
it is a hybrid water heater: a heat pump + one electric heating element – most electric heaters have two heating elements.
Its supposed to be more efficient than normal resistive heating. But of course the initial costs are higher, and its harder to control
it depends on a lot of factors. the basic principle is an ac in reverse, where the efficiency can be greater than 100% as it sucks the heat from the air. well, for some of us, sucking heat from the air can be probamatic, as we may live in a cold climate and we spend a lot of money to heat up our house: for the last four weeks around the new year, I was running around 100gl of heating oil a week.
so this “efficiency gain” can become a major money sucker. unfortunately politicians have decided for me that for large capacitor heaters it is best for me that I use hybrid water heaters.
