My own 35-cents’ worth here … well, I’ve worn aids that many years, so a penny per year isn’t too outlandish.
I found I probably heard sound the most natural and rich with the flesh-colored, plastic, custom molds with a pretty narrow vent hole to prevent occlusion. It seems that style has gone the way of the dodo. What I liked about them was that they sat in the natural cup of the ear - not behind the ear with a mic that points through rustling hair to some point on the ceiling. However, they looked like old-lady fuddy dud, and I had a couple audis tell me I should not even be fit with them any more.
Flash forward to 4 years ago when I started wearing RIE aids with some kind of soft, silicone dome on them. I’ve tried tulip domes, foam/sponge comfort domes, double power domes for old Phonak aids, custom molded silicone tips and now the newer, flatter-style double power dome for the Marvels I have on.
I kid you NOT when I say the style of dome matters a LOT in terms of sound quality. The tulips didn’t give me enough seal for my loss, so I had the same leakage and tinny sound quality. The foam/sponge comfort domes felt DIVINE, but I couldn’t understand anyone talking on the phone. The old double dome power domes I have on my Audeo B’s work super on them, but the sound quality is about 18% less when put on my Marvel aids. The custom molded silicone tips had a vent hole that was first too big, then too small. They also caused compression sores in my ear canals.
To me, there are 4 basic “ends” to a pair of aids: 1.) custom mold will tend to be HARD material or slightly softer silicone, typically either clear, tinted pink or flesh colored, 2.) domes will tend to be made of soft silicone and come in clear or smoke topaz; these can do the job for mild/moderate loss if vented or closed, placed on a receiver that goes IN the ear canal, 3.) double dome "power" domes, which are also made from the softer silicone in clear or smoke topaz, either vented or closed, and are good for moderate/severe loss, and go IN the ear canal, and 4.) custom-molded “tips” which are made big enough to fill the opening of the ear canal with an acorn-sized molded tip that is likely vented to prevent occlusion.
Hope this monograph helps!