Theme the landing page after saving new content
with hook_form_alter you could for the form for the node type add a submit handler that will redirect to a custom page. Alternatively you could use drupal_set_message.

function module_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  if ($form_id == 'the form id for the node form') {
    $form['#submit'][] = 'my_custom_submit_handler';
  }
}

function my_custom_submit_handler(&amp;$form, &amp;$form_state) {
  // Use the drupal_set_message solution.
  drupal_set_message(t('Your Testimonial has been saved!'));
  // Redirect to custom page solution
  $form_state['redirect'] = 'url/to/page';
}