its certainly not a waste of time having one! Have you sen what can be displayed on it? It can show up to 8 different engine stats at once, eliminating need for extra gauges. eg digital water temp, knock level, intake temp, injector duty cycle etc etc... of course you dont need to see all those things, but i love the digital water temp and air intake temp -also you can see your speed, so if you only have the std 180kmh speedo, you can see readings higher than that.
You can easily play with things such as idle speed and rev limit, so for peace of mind if someone else has to drive, set the limiter to 4grand or something then stash the controller!
above all else, they look cool, green backlight, stuck to the dash