Here in italy many and many ppl say "multipower is bad for the shoulder and joints"
What do you think about it?
You'll need to be more specific here. I presume you're talking about this?
If so, then yes, its better used as a coat-rack or pullup bar than for pressing exercises.
If by multi-power you mean smith machine then yes they suck.
Any rull ROM exercise they put a lot of shear forces on the joints. They are also less effective at muscle stimulation and you can't squat as much in them (ironically you can bench more in them if you do free weight pressing).
But please clarify if you mean a smith machine or something else.