A decade ago, Chinese-made (and also Taiwanese-made) products used to have a reputation for poor quality, but there is a lot of truly excellent quality gear being made in China and Taiwan these days - they've really upped their game substantially.
I guess you should also ask someone who's ordered CIEMs from a USA-based lab, such as Ultimate Ears or JHA.
I've personally owned some Unique Melody Miracle CIEMs (made in China) and they were very nicely made.
I also have a pair of Futuresonics MG6 Pro (made in USA) and they were made very badly.
I'm sure you have observed that Noble's CIEMs have quite an enviable reputation for build quality, and they have a lab in China.
As far as US-made CIEMs are concerned, the most obvious flagship competitor to Noble's flagship (K10) would be the JHA Roxanne, so perhaps you could ask some Roxanne owners about the build quality of their US-made Roxannes?
I hope you have a good CIEM experience, regardless of which company or country you order from.
UE stuff is top notch though and their lab is in the US, Roxanne, as its current state is not a fair comparision imo
Good points all around.
I'd say with an actual product (be it tires, speakers, shirts, computer parts, whatever) the location of manufacture could be more significant. Do they have the raw materials locally or do those need to be imported? Is climate a factor? How about qualified technicians to maintain specialized production equipment? What about local shipping reliability? Unions? Taxes?
Some of these factors apply to running a CIEM lab, but some of them don't. I'd think that the process for making CIEMs is similar no matter where the lab is based. It's not a very automated process so once the right equipment is on hand, it comes down to individual skill (which of course is a result of training), along with a good QA process - which in this case doesn't not require anything too amazingly complex.
As a result you end up with Noble and UM (and others) in China, Westone, UE, and 1964 Ears in the USA, Cosmic Ears in Sweden, etc, all having reputations for doing quality work. And there are examples of poor quality from various locations as well.
The trick, I'd say, is making those high quality builds consistent from month to month, year to year. We've seen some brands start out strong and then fizzle out in terms of quality, and some other brands start out humble but eventually become really nice. The other piece of the puzzle is customer service - you can build the best CIEMs ever, but if good communication isn't there, it won't matter. Another piece is speed - nobody wants to wait 12 weeks for their order, although good communication can somewhat mitigate this part.
And then there's the small matter of making your CIEMs actually sound good.
The company that does all the above well (cough... Noble.... cough) will be successful no matter where their lab is based.