Ok, so I have added the plugin and activated it and when navigating to my site I get the landing page properly...How as a developer can I actually view my site as I am working on it within the same server? Is there a "backdoor"?
Yes, just see the configuration of plugin on page Access settings. You can either set "GET parameter". For example if your site is www.example.com and you set GET parameter to soon you will access your site by entering URL www.example.com?soon=1. It will unlock your site for session, means you will se the site unlocked, until you close your browser. This is usefull if you want for example show the site to your client.
For developer more useful is to set his IP address in "IP address" field. For listed IP addreses is site always unlocked.