I would say some vibration is normal, but it shouldn't shake like crazy. Double check that the rubber paddles are properly bolted in and secure and that they're both installed the same way (they're both installed on the correct side of the steel axle). I don't have mine yet so I can't really say I know. :-)
Ego's mowers are extremely smooth operators... they set the bar pretty high. I'm not so sure we should hold a spinning shaft with rubber paddles to the same standard? Obviously, if it's shaking like mad there could be something wrong. If you're really concerned you could compare it to the floor model at your local Home Depot. If they're both similar I wouldn't worry about it.