The ST1903 (TY2903) is a rare movement indeed. Not many people would consider a Chinese made movement 'rare' or even close to rare but nevertheless, it is. Try to find a chronograph movement with a 24Hr sub dial and though they may be out there, they will be very expensive, probably Swiss yes but very expensive. The ST1901 lends itself nicely to those who desire for example, a replica of the Omega Speedmaster or similar but consider this; The speedy has a 12 hr dial so why would anyone want another 12Hr sub dial? The Speedmaster is famous as the 'NASA' watch but I believe a 24Hr sub dial would have been more useful in space and so my replica will have this improved feature all for the low cost of the ST1903 movement.
The movement itself is an accurate time-keeper, has a satisfying 'click' when the column wheel chronograph is operated and is nicely finished. What's not to like?