Honestly, I think customs as a form factor are somewhat overrated in the audiophile community. In my experiences universals can be just as good both in terms of sound quality and isolation, it just depends on the implementation and your own ears! For instance, my ear canals are very narrow and don't bend much. Having tried five different brands over the years, I can say that customs are actually not a great option for me unless they're shallow fit like FitEar. Otherwise they commonly break seal and don't stay in all the way. However some behave better than others: aside from FitEar, the Jerry Harvey ones tend to be among the best for me.

My point is more or less that there's no one-size-fits-all solution, be it a universal or a custom. The idea that it's tailored to your ears would lead you believe it's more of a sure bet in terms of fit and comfort, but you may find, like me, that your ears just don't cooperate as well as others' or that the size of some of these hulking monsters with five bores and multiple crossovers are simply too big. Also the process can become a headache if you need multiple refits. Also consider that with universals you can return or resell them more easily if you find they're not for you.

I'm not trying to scare you away from customs or anything! For some folks they work extremely well, and they're definitely well suited to certain applications (like stage use --- their original purpose). However I tend to be of the mind that they're a little too freely recommended and hyped on that other forum, and as a result some are bitterly disappointed when their expectations aren't met or they end up going through a big ordeal involving multiple returns and taxes.

Also these days I'm firmly of the belief that universals are starting to catch up with customs. The custom fit in and of itself can offer good isolation (for some!) and---in theory---better bottom-end performance. However the primary benefit of customs to my mind was their amorphous body that allowed more drivers and crossovers to be crammed in there. It also allowed for smaller companies to get in on the action without having to invest in design work or OEM manufacturing for complex earpieces. These days however manufacturers have realized that consumers are willing to pay just as much for universal fit versions of such custom-type shells, so this has opened up a whole new realm of pseudo-universal designs. In know some pirates might disagree with me, but in my own experience universals like the FitEar TO GO! 334, F111, Tralucent 1Plus2, and even more "traditional" builds like the Shure SE846 and Final FI-BA-SS can pretty much compete with most CIEMs out there with a few exceptions. For instance stuff by Spiral Ears is pretty advanced, but it won't even fit a lot of peoples' ears due to how many crossover points and bores it has!

Now if they'd just sell the universal UERM commercially, I'd be a happy MuppetFace.