I will give it 5 stars with reservations as I have only had them for one day and I am still testing them, without having placed them in their final positions. Whatever works, works. Similarly, it is value for money and not the typical "Chinese" product. However, the amount of effort required to make it work is another story. I will mention what I remember.

The official instructions for setting up either the screen or the button panel are at least incomplete or inaccurate (possibly due to intermediate firmware upgrades). It is obvious that we need to download the HikConnect app on our mobile phone, but from there on it is chaos. Where do I start...

- The screen can be connected either with Ethernet or with Wi-Fi. We enable DHCP, but the IP addresses below are never updated (unlike some YouTube tutorials), so in the initial phase you don't know if it is connected or not. If you are connected via Wi-Fi, you need to go through the network settings to find your network without knowing if you are connected or not. You tap on the SSID and it gives you options for Reconnect/Disconnect (even though you are already connected) and after pressing Reconnect about ten times, it shows you the IP addresses it has obtained.
- Pressing "Password" in the main settings (not the admin configuration) displays a blank screen that does nothing.
- When you try to change the admin password through the admin configuration, you cannot switch the keyboard to ABC and you can only see numbers and symbols. Also, this specific page is slow and has a lag of seconds. You cannot change the password if you have initially entered letters, so there is an obvious bug here.
- When you try to register the screen on Hik-Connect through the browser, it asks for the famous "Verification Code". Contrary to what is written on official sites, forums, etc., it is NOT printed on the device label, it is not the default ABCDEF, no, no, no... You have to randomly tap on the screen in the empty space between "Verification Code" and the activation button (something that is not at all obvious and I found it by chance on a forum) and set the code there! You enter it in the browser and the registration is completed.
- As for the button panel itself, the first time it needs to be set up with Ethernet (not Wi-Fi). The manual states that it takes the default IP 192.0.0.65/24, but it doesn't work even if you set your network to that subnet. It definitely requires the SADP application (thus Windows), which automatically scans your network and discovers the device (even if it appears to be in a completely different subnet). Through SADP, you activate the button panel, enable its DHCP or change the IP, connect it to Wi-Fi, etc. Of course, the manual doesn't mention anything about SADP, it just tells you to enter the default IP and configure everything from there (which is not true).
- Then you access the web interface of the button panel through the browser (it works with Chrome, not with Firefox...), you definitely do a firmware upgrade because the latest firmware has many improvements: from making the button panel work standalone only through the mobile phone without the internal screen, to lifting an access point if it doesn't find a network, so no cable is needed during the initial setup (and many other changes). Even the firmware upgrade (which is simply referred to as "controller upgrade" in the menu) took me 3-4 attempts to start because it was throwing errors.
Afterwards, you connect the push button to Hik-Connect after sniffing your nails and going to Configuration -> Network -> Advanced -> Platform Access. You search randomly to find the server that works for Greece (since the default does not connect, so we have to manually enter litedev.eu.hik-connect.com), wait for Registration to go Online, and finally Hik-Connect asks for Verification Code again. Which, after a lot of searching, you discover is the... "Stream Encryption/Encryption Key" that you entered on the Platform Access screen.

The above took more than 3-4 hours, so with all that, the devices became registered everywhere and they can see each other (I can also see them from the Hikconnect app on my mobile within or outside the home network).

update: There is more... I want to upgrade the firmware of the monitor. It doesn't seem to have a web interface via IP, so how do I access it? I download and install the iVMS-4200 application from the Hikvision website, add the device based on its IP (because if it is pulled automatically through Hik-Connect, it doesn't allow you to configure anything), guess that for the username I should enter "admin" and the password is what I set for admin on the device through the touch screen, and the firmware update worked perfectly.

Very good choice as long as you find a technician with knowledge, if you take advantage of all the possibilities it can do wonders.
https://youtu.be/aEFpk2nsFdM configuration

In general, bugs will exist in all devices of this type, and that's why companies release firmware to fix them. It would be a shame if they don't, considering the competition in the market. I mention all this because I'm interested in buying it and I'm doing some research.

Update 2:
I'm coming back to talk about the product because I bought it for my country house and I'm very satisfied. The electrician drew a line on the front door and I did the rest myself. The configuration and installation didn't give me any trouble at all. The image is perfect and the mobile application works flawlessly!!

Later, I will also connect it to a lock (Cypriot) and I will have to call an electrician again to provide power from the existing doorbell.

Update 3 14/01/2022:
It works perfectly. I also did an upgrade

If everything they said in the specs was true, it would be fine. Unfortunately, things are not like that.

This particular product has many bugs, so many that it only limits you to basic functions, i.e. pressing the doorbell button and opening the door. HikVision implements its own SIP standard (Video Intercom v2.0 Protocol) for communication between its devices, which is in a primitive stage (they recently added SIP password). It even supports the standard SIP, but many people complain that it doesn't work. Based on the bugs I have seen so far, I have no doubt that it will not be like that.

Therefore, if you are looking for a device that is truly internet-based, look for another company like Fanvil, which exclusively deals with SIP technology (manufactures VoIP phones) and is in the same price range.