Positive review, however - in order to get proper flat signal response and correct bass response, the supplied tips do not give a good enough seal. I replaced the stock tips with the Comply TX-200 filtered tips (sizing between the Sony tips is the same as the Comply sizing), and that made the difference. This review is based on that "modification".
I am a former recording engineer, full time producer, musician and DJ. I have been a big fan of the Sony MDR-7506, MDR-7509, and MDR-7509HD. All of my experiences have been positive with the above products: the signal response is flat, with a little roll off on the low end, but it was consistent, so it could be learned (for mixing and critical listening). The units above were incredibly robust, and I am not ashamed to say I've been incredibly tough on my equipment (in and out of luggage, dropped, neglected, smokey environments, etc.). Also, these are the only cans, except for the AKG K240s (which do not travel well), that could be worn for hours upon hours.
Because of my experience, and because I needed an IEM that could flatly reproduce audio materials and give me the same kind of experience as my other Sony headphones, I bought these.
I'm not disappointed.
Very flat response. Comfortable fit, but I think the nature of IEMs is that they won't be as comfortable as an over the ear studio phone (I can literally forget that the MDR 7509HDs are on my head when I'm in an air conditioned environment) over time. However, portability makes up for the difference.
I would not be afraid to do preliminary audio mixes in these IEMs, or do revision mixes done on Near-fields.
I recommend these if you are looking for something that can give you solid, consistent performance, but at a lower price tag than a custom molded IEM.
Why not five stars: I've worn more comfortable IEMs (consumer grade), and when you have a solid seal, the tips can be irritating after a couple of hours. Also, the stock tips are not usable for flat response (would be fine for casual use, or instances where you need to quickly pull them in and out).
Good luck!