異なる Windows フォーム間でコントロールに効率的にアクセスして変更するにはどうすればよいですか?

    public partial class Form1 : Form
    {
        private void button1_Click(object sender, EventArgs e)
        {
            Form2 frm = new Form2(this);
            frm.Show();
        }

        public string LabelText
        {
            get { return Lbl.Text; }
            set { Lbl.Text = value; }
        }
    }

    public partial class Form2 : Form
    {
        private Form1 mainForm = null;
        public Form2(Form callingForm)
        {
            mainForm = callingForm as Form1; 
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            this.mainForm.LabelText = txtMessage.Text;
        }
    }