Once you have installed a valid SSL certificate on your website, you'll most likely want to ensure that any visitors are accessing your site securely.
HTTP Strict Transport Security is a header that your website can send to visitors to inform them to never connect to your site without encryption for a set time period.
Once an SSL certificate is installed a website displays a certificate, if something is wrong however it won't display this and may warn the site is insecure.
With SNI now widely supported the technical requirement for a dedicated IP address to use SSL/TLS is no longer there and so Freethought no longer provides an IP address free of charge and expects customers to use a shared IP.