PropertyBinding.cs

[HideInInspector] public PropertyInfo   SourceProperty;
[HideInInspector] public PropertyInfo   TargetProperty;

void Start()
{
    SourceProperty.ObserveEveryValueChanged(x => x.GetValue(Source, null)).Subscribe(UpdateTargetProperty);
}

private void UpdateTargetProperty(object value)
{
    if (TargetProperty.PropertyType == typeof(string))
    {
        TargetProperty.SetValue(
            Target,
            string.Format(FormatString, value),
            null
        );
    }
    else //we can assign 1:1
    {
        TargetProperty.SetValue(
            Target,
            value,
            null
        );
    }
}