Okay that it doesn't have a humidity indicator. We can accept the small container.
However, you expect from a modern technology dehumidifier to have (also) the obvious: when the desired humidity limit is reached (which you manually set through selection) to... stop! No, this specific one, as correctly mentioned previously by Nicoleta, continues to operate undeterred in fan mode, producing noise that in my opinion exceeds the old computer fans and is equivalent to an inverter air-conditioner at medium speed.
So how do you know when it has reached the desired humidity? You put your hand on top and if the air is warm and there is a gentle buzzing sound, the dehumidifier is still dehumidifying. When you feel cold air (as mentioned by Nicoleta) and it doesn't have that extra sound I mentioned, it means "mission accomplished"!
I correct a previous user remark and add that in order to "control" it during sleep hours (since it doesn't stop on its own even if it reaches the selected humidity), I use a socket with a simple timer. I select the desired humidity, cut off the power from the timer, and when the dehumidifier receives the command from the timer, it starts in the setting I left it.
It is economical in consumption and relatively quiet.
It is aesthetically pleasing, made with good materials and with a minimum number of buttons, it effectively reduces the humidity for its size.

Edit 05/2018: I come back wiser to finally say that after 2 years of operation, it is going for sale/disposal. Think if you really need a dehumidifier, read and inform yourself. What's the point of operating a dehumidifier for 2 hours in a room to reduce the humidity by 2% and as soon as you open a door or window for a while, the humidity goes back up? Plus, the whole mess that it doesn't shut off on its own, that you can't see the water level, that you can't see the room humidity (you need an extra hygrometer to understand what's happening), and that it doesn't have a sufficient water collection container.

First of all, I would like to thank Nikos2016 for his detailed presentation!

Now, regarding the humidity :( !

I live in a very old house in Nikaia (-+ 65m), despite having insulated the roof, the humidity inside the house is about 15-20% higher than outside (measured with a reliable HAMA meter). As a heating source, I only have 2 inverter a/c units and a gas stove! When I turn on the stove, the whole house gets damp - the aluminum windows fog up and water runs from them, and the tiles in the bathroom get wet, LITERALLY!

On December 31st, I bought the machine and initially set it to full power, and it collected 2+ liters of water every 3 hours! On January 1st, I let it run on low power for 24 hours and it filled two water containers!

And even with the gas stove on, I have no problem! The indoor humidity is 50-53% and the outdoor humidity is 65%+!

P.S. The air in the house has also cleared up!

POSITIVES: The machine is even quieter than the a/c units, even on high power.
It seems to do its job and more.
Nice design and sturdy construction.
Low consumption for its category.
Fair price (there are cheaper options, but much more expensive in the long run).

NEGATIVES: The water tank is opaque (the indicator is not visible at all).
It doesn't have wheels (but it is very light, my wife can lift it for fun).
It doesn't have a humidity display (I wasn't interested in that).

In summary, as they say in my village, it is VALUE FOR MONEY, get it with your eyes closed!

I have the Dehumidifier for 3 weeks (and something).
The humidity in the house was initially 60-65% (since the beginning of October).
With 24-hour operation, it has dropped to 45% (during a rainy period and relative external humidity of 55-65%).
The tank is a bit small (2.1 liters) and I have to empty it twice a day (morning and evening).
The air has "cleared" and is not heavy like before. Before, I used to wake up with a slight stuffiness. Not anymore. I don't know if it's because of the air filter it has, but only the decrease in humidity has improved the microclimate conditions significantly.
Previously, I had the equally efficient but noisy (42dB) and expensive (300Watt) Olimpia Splendid Aquaria 16 dehumidifier.
Pros:
1. Silent operation that does not exceed 35dB next to the device (a 2-year-old computer with two 120mm fans makes the same noise). Even during sleep, it doesn't bother you at all (unless you have it next to your head!!!).
2. Very low power consumption. In the first week, it operated at 160-170 Watts (measured). With humidity below 50% in the house, the consumption does not exceed 155 Watts (Min 150 Watts). That is a cost of around €10 per month with 24-hour operation (e.g., a device with 250Watt - the immediately following one with similar characteristics - costs €17 per month with 24-hour operation in the electricity company).
The specifications state a maximum operation of 210Watt.
3. Small size: You can easily move it wherever you want without difficulty.
4. Sturdy construction without creaking plastics, etc.

Cons:
1. Small tank that you have to empty twice a day depending on the humidity you have.
2. Tank with a dark color that does not help you see the water level that has accumulated.
3. In case of a power outage, it does not start automatically, and if you start it manually, it starts with the clothes drying setting and not the program you had it on. You will have to adjust it manually.
4. It does not have a built-in humidity meter (relevant because I did not prefer it). The humidity near the device definitely does not reflect the actual humidity, for example, 5 meters away from the device. Personally, I have two humidity meters placed in diametrically opposite points in the house to calculate the humidity.
5. It does not have a timer (for those who prefer it). Personally, I do not consider it a negative because the partial operation of the dehumidifier in a house with humidity is useless, and considering its cost-effectiveness.

General observations:
Although it is a model from the previous year, it does its job very well in a house up to 70 square meters.
The negatives I mentioned above do not make me regret the purchase I made. For a larger house, I would recommend buying two of these devices for distribution and maximizing performance (although it will cost a bit more to buy them). In a house with specific layout (hallways, etc.), do not expect ANY dehumidifier to do a good job, no matter how good and expensive it is, in a fixed position (from experience).
In relation to its price, which is a bit high and initially gave me doubts, the operating cost will be recovered within a year compared to buying another similar device that is €70 cheaper but consumes 250 Watts.
I highly recommend it!!!
P.S. I hope I helped those who are looking because when I was searching for information before the purchase, I could only find a few and incomplete ones.