I'd say a large percentage of anything requiring precise machining, and to be robust, is not going to be good on Aliexpress. Rings, scopes, bipods come to mind here.
I've had a AR15 handguard from Aliexpress that worked just fine (I did not use the supplied barrel nut, as I did not want to die), as well as things like gun cases, shooting mats.
At the other end of the scale are Maxtoch lights, which seem to buck the trend of cheap and nasty product on Aliexpress.
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