customer access for new site in a multisite installation

We run a multisite with sites for different customers. Which plugin you would recommend to show a preview of a new site to our customer with a login? I use a Maintenance Mode plugin at this time which does not work well with a multisite installation. The customer has to be logged in as an admin or editor to see the site. I like to use a plugin were the customer can look at his new site without seeing the wp admin menu. Thanks for your help. Regards Andreas