Every mechanical timepiece requires servicing every three to five years. The oil inside the watch slowly evaporates and what remains is sticky gum. As long as you service the watches every several years, they should last long enough to be heirlooms. In the worst case, and a china clone watch fails without availability of parts, a genuine swiss ETA movement will drop in to replace it without any hassle.
There is no significant difference between the china clone ETA movements and genuine ETA movements. You may have noticed that a couple of months ago, a "super clone" was released. They cost more but claim to be 1:1 with full interchange of all parts.
Regarding quality, you have to read the dealer advertisement or ask them in email. For the DSSD you want, the major difference is that some of the A21j models come with glass crystals instead of sapphire crystals.
The rest of the watch is not "better" between the different movement options. That practice ended a few years ago. If you buy an Asian ETA or a Swiss ETA from the same factory, the watch will be the same watch and the price difference is purely due to the movement inside.
Finally, a word about QC. There is none at the factories. If you buy 2 of the same watch, one might be perfect and one might fall apart on day 2. That is why you buy from a trusted dealer. Forum dealers will make this kind of problem right for you. Their track record of customer service and "honesty" are why we keep them on the forum.