Well, if you really think about it, IEMS are not really worth it just for their lack of sound leakage or any other single quality I am going to rage on IEMs right now, so please forgive me. lol
IEMs do not leak sound when they are in your ear canal. Your ears are not designed to be plugged completely and be isolated in such a way, your ear workings are especially not designed to pick up audio piped directly into your ear canal. IEMS over time will damage your ears much faster than any other type of headphone. They are never comfortable and people who say they are, are just speaking nonsense. There is something jammed into your ear, how is that comfortable? Almost all customs some most high quality sets wrap over the top of your ear? It's extremely annoying and often the cord will flip up and not conform to your ear. You need to keep your source in a place below you to literally keep tension on the wire and cable to conform to the back side of your ear so it stays in place. This is just the dumbest thing to me and I really do not understand it. Here is a freebie to the audio companies who make customs.
Put some type of conforming material over the ends of the iem cable closest to the drivers that can be molded and shaped repeatedly. I've seen dirt cheap material that does this, very pipe cleaner-ish. When you bend it, it will stay that way. Only the first few inches closest to the drivers need to have this type of material over it, this would allow for excellent comfort and removes the constant motion of the iem cable over the backside of your ear, it often flops up and moves around and bunches up. This is pure nonsense, fix it lol.
Having said that, normal hanging style earbuds are much safer to listen to and new sets like the 9wave installed a great standing wave avoidance feature. Like ultrasones s logic sort of, its much safer to listen to than any earbud in existence that I am aware of. With that, the soundstage is much larger, spacious and more natural sounding. Not only that, they are more comfortable. All of that to me is worth more than worrying about sound leakage. If people dont like your music, tell them to take a hike and go buy some earplugs heh. Why damage your ears just so someone nearby doesnt get annoyed by your music that is only barely audible to being with