Am no follower of the Pomodoro technique nor do I know its specifics but before you go ahead and try out those multiple Adobe AIR applications or use the GNOME-oriented Workrave, please try out this software called RSIBreak which was built for KDE specifically.
RSIBreak - Repetitive Strain Injury prevention software for KDE
It isn’t a full fledged timer feature but I think it will get your needs covered with its offerings easily enough. One of the amazing utilities I’ve used, built with KDE Libraries. It should be available in your Linux distribution’s software repository too.
