So I ordered one of both. 6.3 in USDM, 5.5 in Japan reel

Here is what I noticed:

Both so far have been terrific and smooth drag is a feature that is a big step up from the past model.
-Weight is less in JDM due to the Aluminum vs Brass gear. I do notice that the Japan model is lighter but only slightly. Both are very light.
- Japan has tighter tolerances and is smoother. Some of that is probably the gear but there are also small differences on other parts. Such as the Spool spins more freely in JDM with all breaks off. JDM feels more finesse.
- The USDM has a more solid feeling when reeling. JDM has a more hollow feel.

if you are going to use lighter baits 1/2 oz and under I would go with Japan version.
If you are throwing spinnerbaits , Flippin or using it for deeper crank baits go with US version.

Both reels Daiwa I feel hit it out of the park. Casting distance over most other Daiwa reels I have is 10%+.
I can skip with this no problem. You have to dial it in a little bit more than Tatula Sv because the new boost breaking system. However the new Zillion will smoke the Tatula Sv in distance casting.

One last thing is I have noticed my accuracy is far better with this reel. That to me is probably the biggest benefit overall. I would say my casting accuracy circle is about 1/2 as big in variance and that was near right out of the box.

For me the new Zillion is living up to the hype.