I don't know about the difficulty, but you can look at the complexity of this ETA 6497 movement on GrabCAD [0]. After seeing this a while ago, it made sense to

I don't know about the difficulty, but you can look at the complexity of this ETA 6497 movement on GrabCAD [0]. After seeing this a while ago, it made sense to me why small/new brands generally use a Seiko NH35 or something similar that they can buy in bulk. [0] https://grabcad.com/library/eta-6497-1-complete-watch-movement https://grabcad.com/library/eta-6497-1-complete-watch-moveme...