The materials that are used for the casing, bracelet, and exterior features of both types of watch are the same. The only difference is in the precision of the manufacturing. Some exterior details may be closer to the original and the exterior features of the watch may be more exact on the Swiss models.
The biggest difference between Swiss and Japanese quality is the mechanism itself. Swiss quality watches are made with Swiss ETA movement and are actually made in Switzerland. They are identical to the original in every way. Japanese quality watches are made with Miyota movement. This mechanism can sometimes be less precise.
On Japanese quality watches the chronograph feature is sometimes just for show.
On Swiss quality watches the power reserve is better so it will need to be wound less.
Although some sites may make a claim their replica watches are water proof no replica watch is water proof. They are water resistant. This means you cannot submerge your watch in water and you should remove it before taking a shower.