The differences between Swiss and Japanese movements are mostly that Swiss movements are typically more aesthetically designed, whereas Japanese movements are built more with precision and accuracy in mind. Both are used to power watches of all different kinds, and used by many watchmakers around the world.
For simplicity, we’ll stick to the two leading mechanical movement manufacturers, ETA SA from Switzerland, and Miyota from Japan. While the initial purpose end result of any mechanical movements are identical, with different companies comes a huge variety of different styles, types, parts, all-sorts. A good quality movement will last a lifetime and longer with proper care, and the standards held by ETA and Miyota movements are testament to this.
Swiss movements are held in high regard by many watchmakers, and collectors, for a multitude of reasons. ETA mechanical parts are, for the most part, manufactured with a little more flair than others. Decoration is a large part of Swiss mechanisms, from the way the metals are cut, to the colour of the jewels, every aesthetic detail is thought of during the design and build process. The Swiss do, for the most part, still use hand assembly for some calibre models, which can affect the price of the movements.
Japanese movements are manufactured slightly differently, mostly in an automated robotics line, but this allows for a much lower degree of error than by eye alone. While not a huge amount of detailing is put into most Miyota movements, the slightly more “raw” look of the pure mechanical parts does appeal to a lot of people. Due to the nature of the assembly, the price of Japanese movements is often cheaper than Swiss, but this does in no way indicate lower quality.
It’s difficult to directly compare Swiss vs Japanese movements due to the sheer number of variables in the design, manufacture, assembly, decoration, and style of each piece. With some Swiss movements, there are multiple versions of the same calibre, for example the famous Swiss ETA Valjoux 7750 movement comes in several grades that increase in price for better parts and decoration. While the same cannot be said for Japanese movements on the whole, the style and price of them often means it’s possible to upgrade the entire mechanism instead.