Update 17/1/2025 (2.5 years of use): It started disconnecting on a daily basis, at least 2-3 times a day. Not only does it disconnect, but it also requires re-unpairing and pairing, meaning I have to set it up from scratch again. I’ve made the decision and instead of spending 50 euros on powerline, I will get a hammer drill to dig through the wall to run a spiral and inside it an ethernet cable to create my own socket. It costs twice as much since afterwards it needs plastering and painting the wall, but it is the only sure solution.
I chose this one because the TL-PA4010P Kit left me after almost 2 years of use. It wouldn’t sync with anything, after disconnecting one of the two from the socket where I had it, no matter what I did (pair, factory reset, same room, different computer, different house - yes, I tried that too), so I came here with a refund.
For two weeks, I used 20 meters of cat.6 Ethernet from the living room where the OTE router-modem is to my room, on the computer. As you can see in the upper part of the photo and then in the lower part, the loss is zero. There was a noticeable increase in ping, but I wouldn’t even call that a "problem" since I didn’t notice any issues in games. If you live in an old house (construction from the 50s-60s usually) and the electrical wiring hasn’t been changed at all from the panel to the actual power cables inside the wall, it’s very likely that it won’t work for you, or if it does, you’ll have terrible losses.
The ideal solution, as a friend who is an electrician and has a hobby of installing home networks told me verbatim, is: during a renovation, the owner should install UTP (cat.6e/cat 7) (https://www.skroutz.gr/s/10804368/Powertech-U-UTP-Cat-6e-Cable-100m-%CE%9C%CE%B1%CF%8D%CF%81%CE%BF-CAB-N061.html) inside the wall and bring out Ethernet ports (https://www.skroutz.gr/s/24031827/DeLock-%CE%94%CE%B9%CF%80%CE%BB%CE%AE-%CE%A0%CF%81%CE%AF%CE%B6%CE%B1-%CE%94%CE%B9%CE%BA%CF%84%CF%8D%CE%BF%CF%85-RJ45-%CE%BC%CE%B5-%CE%A0%CE%BB%CE%B1%CE%AF%CF%83%CE%B9%CE%BF-%CE%A4%CF%8D%CF%80%CE%BF%CF%85-Cat6-%CF%83%CE%B5-%CE%9B%CE%B5%CF%85%CE%BA%CF%8C-%CE%A7%CF%81%CF%8E%CE%BC%CE%B1-86195.html) throughout the house where needed, meaning bedroom, living room. The solution provided by powerline is something that often fails (not frequently over the years) and is not 100% reliable; for example, a lightning strike can easily burn them out. I mention this mainly for people who are considering renovating or are renovating a space and need a wired connection (working from home, online games, streaming, transferring large amounts of files, etc.). The above endeavor will cost you about as much as 2 or 3 powerline devices since it includes labor for installation, cable, and sockets. However, it won’t be affected by earthquakes, humidity, or anything. It lasts as long as your building does!
In summary, I recommend this one since it is a newer series of the most popular "grandmother," I would say, TL-PA4010P.
Update 29/8/2023: After 50 meters of Ethernet providing internet to a TP-LINK Archer AX73 v1, I now have the powerline bringing internet to the computer (20-25 meters of electrical wiring - 1 room next door). The speeds, as you can see in the photo, are now 93 down/10 up.
Update 24/5/2024: I’m removing one star because after upgrading to a 200/20 ftth line, the speed I’m getting is 90 download 20 upload. The motherboard port supports up to 1Gbp/s so this is definitely not the issue.