I do, you have to go to a doctor (in the US) for these and get fitted it's not cheap and these IEMs tend to cost more as well. Pain in the ass to insert as well.
Ultimately you're shelling out for a better seal. It's worth it, with a catch. You can get a "perfect seal" with non custom IEMs if you are willing to faff about and fuck about with tips and other items and find at set that works for you. Or just go etymotic and rape your ears, and even they will make you a custom tip. For me I'm a giant, go go Dutch blood though I'm American! So I'm tall as fuck, former military, and buit like a damn tank. Even the large foams and silicon tips don't fit me, too small. So I get the XLs and very few brands make those and they are a pain to hunt down.
The last customs I got ran me about 3k, 64 audio. The issue is the custom factor drives the price up enough it's go big or go home. And the brands that do offer this are all to quick to sell you some 18 driver monster that doesn't really compete with a 300 buck blessing 2 or a 1000 buck shure 846. Both of those sort of define where you want to be.
curious as to what brands you jumped on