Is Mac Informer safe?
Applications bought through the Mac App Store are handled by Apple's mechanism. Most non-App Store Mac applications include their own built-in software updating mechanisms.

I would approach this as a question of what value does Mac Informer offer over the risk of opening up your Mac to an unknown company.

At some stage, the application will need your administrator privileges to install software updates. This will expose your Mac to any actions, positive or negative, the application wishes to take.

The lack of identifiable individuals, lack of physical address, and lack of registered company details on the about page does concern me.