The hub on the Eclipse is 92mm wide (bearing to bearing) versus the standard 100mm. I imagine the frame has to be about 8mm narrower to allow it. This won’t really affect your ability to stand on the cranks, but it appears to be a unicycle for freestyle, not flatland. The narrower hub will result in (hopefully) less of a wobble as the wheel turns. If you consider… having the mass of the cranks/pedals closer to the middle will reduce the Q factor you experience while riding.
I hope this helps. That unicycle looks sweet. I’ve always wanted a freestyle uni but I seem to be able to do tricks well enough on the KH20. Although I imagine it helps to make the tricks look cleaner. Additionally, shorter crank arms mean less of a leg arc… which I’m sure helps a lot for stability.