I came back with some new data after a while of playing with this toy.
For the first time when I took it outdoor I have noticed that it has the tendency to go up very fast, despite to the fact that I didn't pushed the throttle not even half way. Another issue is the fact that this helicopter cannot be controlled at all, even in the softest breeze. The first big crash happened in a very strange way: It was quite high (as it wanted to be), pushing the lever forward, the tail raised a little bit and the main blades smashed into its own body. I couldn't believe when I saw some pieces from it flying around and the main body smashing on the ground.
The good part (...) is that it resisted to this serious impact. It lost some parts (weights, leads and screws) from the flying bar. I ordered the parts and I took it again outdoor.
After a few difficult low flights, it suddenly went up at around 30m height, without any response to my commends.
I lowerred the throttle to almost zero, with no response. After a few desperate manouvers it started to descent and finaly landed in one piece.
Meanwhile, I ordered another helicopter, made by professionals, which brought me a real flying experience.
About Syma S031 G...is a toy, as is correctly mentioned on this site. It can be the first step into this hobby, but not more. However, I will keep it on a shelf, just for display.