These monitors were my personal choice based on reputation, quality, and performance (however perceived it may be since i've never actually listened to a custom Westone) of Westone products in my personal experience. Their customer support really blew me away the first time i spoke with them, and i have been using their UM1s for the better part of 3 months. The fact that a single driver headphone is capable of handling so much volume input on stage is simply astounding to me. With that said, i wanted more bass response for my personal listening while still gaining more headroom for the stage and the ES2s were the next logical step after i had decided that squeezing the foam tips everytime i had to remove the phones from my head at work was not worth the hassle any longer.
I am not an expert in either brand's (JHA/Westone) performance or quality, but my ultimate decision was based on two important (to me) things. I did in fact contact JHA asking about their products via email. The response i got was very informative but i didn't get the warm fuzzy that i always look for when purchasing big ticket items. The second issue i had was that they did not have an audiologist in the Dallas/Fort Worth area they recommended, and as such i was leary about finding one on my own because i've read multiple negative posts about choosing an audiologist that isn't familiar with an IEM brand's product. It was just the opposite on both accounts when i contacted Westone.
Long story short: Westone comes very highly recommended in comfort, quality, reputation, and performance. I can comment directly on their reputation and performance. Also, the part of the IEM that gets inserted in your ear canal is a heat activated material that expands slightly once in contact with the skin. That doesn't hurt either. It's the best compromise between a fully acrylic shell and a fully silicone shell. Hope that clears something up for those of you who have viewed this post.
