Asynchronouse file download with WebRequest + show progress in Progress bar. APM vs async/await

gistfile1.cs

#######################################
                   APM
#######################################

    public partial class APMVersion : Form
    {
        private const int BUFFER_SIZE = 1024;

        public Form1()
        {
            InitializeComponent();
        }

        private void ManipulateUI(Action action)
        {
            this.Invoke(action);
        }

        private void button1_Click(object sender, EventArgs e)
        {
            var url = this.textBox1.Text;
            if (String.IsNullOrEmpty(url))
            {
                return;
            }

            this.button1.Enabled = false;
            var webRequest = WebRequest.Create(url);
            webRequest.BeginGetResponse(iar =>
            {
                var response = webRequest.EndGetResponse(iar);
                var contentLength = (int)response.ContentLength;
                ManipulateUI(() => this.progressBar1.Maximum = contentLength);
                var stream = response.GetResponseStream();
                var bytes = new byte[BUFFER_SIZE];
                var state = new DownloadFileRequestState { Stream = stream, Bytes = bytes, Url = url };
                stream.BeginRead(bytes, 0, BUFFER_SIZE, ReadCallback, state);
            }, null);
        }

        private void ReadCallback(IAsyncResult iAsyncResult)
        {
            var state = (DownloadFileRequestState)iAsyncResult.AsyncState;
            var stream = state.Stream;
            var bytesRead = stream.EndRead(iAsyncResult);
            if (bytesRead > 0)
            {
                this.ManipulateUI(() => this.progressBar1.Increment(bytesRead));
                state.AllBytes.AddRange(state.Bytes.Take(bytesRead));
                stream.BeginRead(state.Bytes, 0, BUFFER_SIZE, ReadCallback, state);
            }
            else
            {
                var fileName = Path.GetFileName(state.Url);
                File.WriteAllBytes(fileName, state.AllBytes.ToArray());
                this.ManipulateUI(() => this.button1.Enabled = true);
            }
        }

        private class DownloadFileRequestState
        {
            public DownloadFileRequestState()
            {
                this.AllBytes = new List<byte>();
            }

            public List<byte> AllBytes { get; private set; }
            public Stream Stream { get; set; }
            public byte[] Bytes { get; set; }
            public string Url { get; set; }
        }
    }

#######################################
             async/await
#######################################

    public partial class DownloadSpeedAsync : Form
    {
        private const int BUFFER_SIZE = 1024;

        public DownloadSpeedAsync()
        {
            InitializeComponent();
        }

        private async void button1_Click(object sender, EventArgs e)
        {
            var url = this.textBox1.Text;
            if (String.IsNullOrEmpty(url))
            {
                return;
            }

            this.button1.Enabled = false;
            var webRequest = WebRequest.Create(url);
            var response = await webRequest.GetResponseAsync();
            this.progressBar1.Maximum = (int)response.ContentLength;
            var list = new List<byte>();
            var bytes = new byte[BUFFER_SIZE];
            var stream = response.GetResponseStream();
            
            int bytesRead = 0;
            do
            {
                bytesRead = await stream.ReadAsync(bytes, 0, BUFFER_SIZE);
                list.AddRange(bytes.Take(bytesRead));
                this.progressBar1.Increment(bytesRead);
            } while (bytesRead > 0);

            var fileName = Path.GetFileName(url);
            File.WriteAllBytes(fileName, list.ToArray());
            this.button1.Enabled = true;
        }
    }