Should I use the Thank You page of Fluttermail or my own Thank You page for newsletter signups?

You have the option to use either the Fluttermail thank you page or your own thank you page.

But we strongly recommend using your own thank you page for the visitor to be brought back to your site. If you use Fluttermail's Thank You page, the visitor will be redirected to the Fluttermail website.

Another advantage of using your own thank you page is that you will be able to customize it.