This mod received a major overhaul in version 2.0.0, solving the issue of item entity age desynchronization in multiplayer. This means that to ensure synchronized despawn warnings in multiplayer, the mod must now (2.0.0+) be installed on both the client and the server.
Additionally, a new fade-in/fade-out mode has been added, making the flashing effect appear more natural.
(Of course, if you're playing in singleplayer, there's no need to worry about this.)