How to configure a "work in progress" page

I am working on a WP site in which I installed "Maintenance mode" plugin to avoid the site being visible before the work it's done.

Then I installed wpmu dev Dashboard, and tried to install WPMUDEV plug-ins, but the installation gives me an error (it seems it's not compatible with Maintenance Mode and asks me to deactivate it).

How can I fix this?
Is there a different plug-in in your library that could do the same thing as Maintenance Mode (adding a temporary front page before the work on the backend is done)?

Thanks a lot