They look similar to custom-molded in-ear monitors from Ultimate Ears and Westone, but the StageDivers are universal-fit models that come with silicone ear tips. The large earpieces rest on the folds of your outer ear, so the fit feels more secure than in-ears that stick out from your ears. Both InEar models have user replaceable cables, and both are balanced armature designs. The StageDiver 2 has two drivers, while the StageDiver 3 has three.
The sound is remarkably clear, but never lean or bass light. There's an open quality to the imaging I find attractive, and I could keep the StageDiver 2 in my ears for hours at a time without ever feeling fatigued. I listened to both StageDivers for several weeks -- that's longer than I usually have time for -- and was consistently impressed by their sound.
Next, I directly compared the StageDiver 2 with a custom $399 Ultimate Ears 4 Pro headphone that are molded to my ears. Both models use dual balanced armature drivers, so it was a fair match. First thing, the UE 4 Pro definitely produces better isolation from environmental noise, but purchasing any custom molded headphone requires a visit to an audiologist to make ear molds, and that usually runs $50 to $75. That's not required with the Stagedivers -- just pop on the silicone tips and you're good to go.
The UE 4 Pro sounds perfectly clear, but the StageDiver 2 has more "juice." Its richer and warmer balance flatters all types of music. Voices sound more natural; they have more body, and the bass and drums pack more of a wallop. Then there's the stereo imaging: it's wider and more spacious over the StageDiver 2. So other than isolation from noise, the StageDiver 2 outshined the UE 4 Pro in every way.
Next up, I pitted the StageDiver 2 against one of my reference in-ears, the custom-molded Jerry Harvey JH-13 ($1,099). That one was more transparent and pure sounding, but the StageDiver 2's richer tonal balance was still impressive. Moving up to the StageDiver 3 warmed up the balance even more, so if you like to really feel the bass, go for the StageDiver 3. The bass isn't muddy or bloated, there's just more of it. The StageDriver 3's big, wide-open imaging doesn't bunch up the sound inside your head. I'm not a bass freak, so I'd stick with the StageDiver 2. The JH-13 is better overall, but it's more than double the price of the StageDiver 2.