Hi André.
It's been a while sinse I played the demo but I'll try and answer. The buzzer means you got several combinations wrong. Get too many wrong and you lose, get a perfect score and you'll be told so.
I encountered no problem with the keys, however if you don't hit them in rythm you won't get your hero saying "punch" or whatever, and will just hear nothing, and that combination will count as wrong.
As to the robots, I don't remember them requiring anything special other than hitting the keys in time like everyone else in the game, though i do remember the timings got quite interesting.
Unfortunately there isn't a new version of the game. last I heard the developer hadn't abandoned the idea and was even considering something for Ios, but had personal and family things on hand so didn't know where or how the project was going, it has been a while now I admit, but I wouldn't counthe developer out just yet as in the past developers have occasionally surprised with a new version late after the first.
With our dreaming and singing, Ceaseless and sorrowless we! The glory about us clinging Of the glorious futures we see,
Our souls with high music ringing; O men! It must ever be
That we dwell in our dreaming and singing, A little apart from ye. (Arthur O'Shaughnessy 1873.)