Given that there's been some discussion lately about chromo movements, especially comparing the ETA-Valjoux 7750 movement used in earlier IWC chronos (like Porsche Design) ones to IWC's modern in-house Calibre 8936x, I thought a few technical words might be helpful:
First, on general function the 7750 is considered, within the industry, as a "tractor". It is an extremely durable and well-functioning movement. Its basic design is used as a starting point in the design of several other movements, including most recently a limited production time-only movement produced by an Austrian watchmaker.
On "optics" --how the movement appears, the 7750 is not considered as especially attractive. This is one reason that you seldom see the movement behind a display back. In my opinion, you shouldn't necessarily get fooled by plating or blued-screws. On the latter, there are two ways of producing them --dipping them in a chemical bath (almost like painting them) or having each screw heat-treated until the metal turns blue. The look is virtually the same, but from an artisan perspective the chemical treating isn't considered as special. On plating, it's easy to do and costs a few cents. Gold plating isn't materially more expensive than, say, nickel plating and probably less costly (but again within a few cents) of rhodium plating. The old pocket watch movements usually used brass bridges without plating, and they both work fine but have survived for many decades.
On movement decoration, most of the difference here is simply optics. To those who don't like the appearance of the 7750 (with its cams and springs) the decoration really is like making a silk purse out of a sow's ear. But to me, I think some decoration can be visually special. Anglage, the polishing of edges, is important but subtle (and most movements today, except very high end ones, use "stamped" anglage). I personally like perlage, those little circles, and stripes can be nice. There are may forms of movement decoration, and you can find more by searching on the Net.
Finally, and this the big finally-- movement design is important to purists, specially that more expensive chronographs use a column wheel. In the early days of this forum, I staunchly defended the 7750's design vs. the classical column-wheel chronograph design, since the differences are subtle. One writer describes the differences as follows:
"Column wheel movements are expensive to produce and require very fine adjustment to function properly, so for mass-produced inexpensive movements a simpler solution was required. Several options were introduced; the most popular are cam and lever (or coulisse), and shuttle cam (or navette). Essentially they replace the column wheel with a series of levers, pawls and arms that mesh together with an eccentric cam. Adjustment and repair is much simpler and production is cheaper too, as the tolerances can be a little looser than in a column wheel. While not really any “worse” than a column wheel (the simpler repair is certainly a plus), modern tastes and marketing have made column wheel designs the top tier of chronographs and workhorse lever-actuated movements have become common in less expensive mass-produced watches. The ubiquitous Valjoux 7750 uses cam and lever, while Lemania-based calibres often have navette systems."
There are functional differences as well. Many cam-designed chronos have a jump when they start which will be avoided with a column wheel. Also a column wheel design allows for the use of a "vertical clutch" which allows the movement to avoid losing amplitude when the chrono is running --in theory avoiding any difference (usually relatively small) in accuracy over extended periods of chrono use. You can tell a column wheel from a mile away, and a nice image shown on World Tempus (not of an IWC movement) is this one, with blue added:
