Funny. I've had some really bad experiences with FutureSonics shell lab, and so has another of our members here on Head-Fi.
UM are not alone.
Just sayin', is all.
Therefore, King8888, I wouldn't necessarily be too put off about UM, from the standpoint that whoever you buy a CIEM from, it basically depends upon the individual member of staff who randomly happens to be allocated to work on your CIEM shells. All the CIEM vendors produce some good stuff and, occasionally, some less acceptable stuff. All the CIEM vendors have staff come and go, and thus occasional influx of new staff who may be less experienced. I'm not saying any of this to 'stick up for UM'; I'm merely pointing out that no lab/vendor always produces flawless work; it's luck of the draw, sometimes. I've had good and bad from UM and I've had good and bad from FS. Eventually, even the likes of Heir may slip from their pedestal. The very nature of CIEM manufacture is that it is an artform and requires human skill rather than being made entirely by machine (although, with the onward march of 3-D printing, this may change within the next couple of years).
I used to make high-class furniture and both myself and my colleagues would openly admit to each other (& ourselves) that some of our pieces were of a superior standard of craftsmanship to other pieces we'd made. This was never deliberate, it was just that sometimes the making of a piece would 'flow' and at other times mistakes would happen due to accidents or due to lapses of concentration, or to troublesome imperfections in materials.
In short, I would choose your CIEMs on the basis of which one you think is most likely to meet your requirements in terms of sound characteristics. Almost all the vendors/labs (including UM) can produce superb quality CIEMs and there is an entirely good chance that you'll be very happy with the quality of what you receive. If you happen to be unlucky, with whatever lab/vendor you buy from, then yes it's inconvenient but it's not the end of the world - there's a 30-day free remould policy for almost all CIEM vendors. No one likes the hassle and expense of this - not even the labs themselves, but that's just life. NO vendor is 'immune' to problems.
