I ordered the Large size, 1.78 height, 81 kilograms. It fits fine around the waist, but it needs to be shortened by about 2 centimeters.
The construction is quite standard, with buttons instead of a zipper in the front and adjustable straps at the waist. I didn't see any poor quality stitching on mine, quite the opposite. The fabric is of good quality. It is neither thin nor thick, it has a very slight stiffness, probably due to its waterproofing. The comfort it provides is not affected at all and the pockets - all of them close with buttons - are in the right places.
For €20-25, there's no question that it's worth it. What remains to be seen is its durability over time, so I will come back to that.

The positive thing it has is the texture of the fabric, it looks nice. Another positive thing is that it is waterproof. Otherwise, it is not worth paying more than 20 euros for this pair of pants. Find the cheapest store if you want to buy it. Its seams are not good and there are many loose threads in many places, it doesn't seem durable. In fact, I bought two together (in the same order), one olive color and the other dark blue, and they were both of the same quality. I don't know if I happened to get "problematic" pieces, but their price justifies it.
In summary: a mediocre purchase but you get what you pay for (I bought it for 19 euros).