They are quite interesting. I compared them to the Klipsch Image and although they don't have the bass control of the Images, they do sound well. I won't say their sound compares to the Images, both are single BA canalphones at approximately the same shape and size, they don't, but they do have a unique sound sonic character. It's going to take awhile to fully appreciate these just like it took awhile to appreciate the Images.
Right now I'd say their sound is much more forward and harsh than the Images...this assessment is with the EQ of the source at full flat and with minimal sound enhancements. I tried them earlier and set the EQ to what I like while using the Denon 751s. However, after using these for quite a while I put in the Images and reset the EQ to flat. The Images blew me away by the bass control...just more than amazing, astounding, would be a better word...and continued to listen to them for awhile.
I decided to put these ER4Ps back in and left the EQ at flat. I'm going to put the EQ back to what it was earlier because there's just a bit of harshness and edge to the highs. The mids seem perfect and the low end, not necessarily plentiful but, is well controlled. Not even close to the control of the Images, though.
But, like I said, it will take some time for me to fully realize the quality of sound these ER4Ps have. The Images, when I first received them and for a few days afterwards, weren't apparent to me how well engineered they were. These ER4Ps might blow me away like these Images recently did.