Sure, every setting in the Customizer is saved either as a theme mod (by default) or option (if you set the ‘type’ to ‘option’ in $wp_customize->add_setting()).
You can access the user-defined value using get_theme_mod() (or get_option()).
In your example, the value you are looking for can be retrieved with:
$downloads_tab_text = get_theme_mod( 'product-downloads-tab' );