A properly running a21j, china ETA or Swiss ETA should be serviced every 3 to 5 years to replace the oil as it dries up and turns to gum.
If you do that, the watch should last years and years. The a21j is a copy of the very solid Japanese Citizen Watch workhorse.
Crappy, questionable "mystery movements" that break like the wind don't (or should not) exist in the reps we buy here. They are relegated to watches you buy on the street from a guy with a suitcase.
To get to the trusted dealer list, just go out to the forum main page. The one with the chat box at the top. Scroll about halfway down. Easy.
There are four trusted techs in the USA and one in Canada. There are others throughout the world.