Greenwings are generally fairly mellow. BUT some males can have dominance issues...
The biggest issue with any large macaws are socialization issues. Macaws, like conures, are pair bond birds. If they are not handled by more than one person, they tend to pair up and become difficult for others to handle. If they are socialized with everyone, then generally everyone will be able to handle them...
The other thing you absolutely DO NOT DO with any large macaw is show fear. That can trigger dominance issues even where there are none. Macaws sometimes like to play the "made you jump" game... If it doesn't work, they stop doing it. If they get high drama as a reward, it becomes something they do all the time.
I beak wrestle with my greenwing nose to beak all the time. They really are gentle by nature IF PROPERLY SOCIALIZED... if not, then be careful... especially with small children around.
A properly socialized greening?! I often wonder how it's possible to love a bird this much... or be loved by a bird this much. BONDED works both ways.