Quarter or Half

Well, obviously there are differences. One would have to evaluate the space anyway. 'Not that big' can mean several things. For me, 'not that big' could be 50 sqm, for others 10sqm. What area are we talking about? In a 10 sqm room, absurdly enough, a baby grand might sound better depending on the acoustics. With a grand piano you would have a more beautiful base sound, but the sound would bounce everywhere making you uncomfortable during performance, so you would have to treat the room and absorb a lot.

I agree with Simone! It should be added that the larger the piano, the longer the key leverage, resulting in more refined dynamic control.

On the quarter grand, I recommend the Yamaha C1, with very high performance.

In reality it is a very small bedroom and the fourth one is definitely better ...I wanted to know if the mechanism is similar

And what do you think about a Hermann quarter grand? I don't know the brand