The Concept Z has been one those things we see occasionally that really, really get over-hyped, over-sold. There are usually several each year in different categories. Then, they hit the market, the pre-release hype dies away to reality.
So far, most of the reviews have mentioned one issue or another with the Concept Z, say like noise and vibration. And, tests of casting distance have shown it not to be superior to others as was suggested before its release.
So, for me, there'd be no contest . . . today. You have a reliable winner in a Shimano versus a greater unknown. A year from now, it could be the Concept Z will have proven itself out in real time situations.
But, if you are buying today? Take the safer road.