I found an insteresting item in Ali-Express, ER610 of EARMAX – audio product manufacturer of China – and it seems to be used for dual balanced armature transducer(driver) in each units of left and right.
I can find an image for used Knowles B.A unit in their sales page: 
And there’s product number: K30265 by idendified with graphical adjust.
So I reached their information page of Knowles, http://www.knowles.com/eng/Products/Receivers-and-speakers/Hearing-instruments/DTEC-series# and here http://kr.mouser.com/ProductDetail/Knowles/dtec-30265-000/?qs=CwrZmfgQ%2F8PExkdM0ny2Cg%3D%3D
It seems old-aged transducer type as I know before, and I can check RMS test result in their specification documents:
As their result, I can conjecture this IEM sound will enough to feeling in low to middle frequency, but less high frequency in non-tuned. Its response frequency impedence graph is like this:
By impedence, it looks result for dual armatures, there’s deep reverse peak in 1400 to 1500. It means smoothness is may less than normal single balanced armature.
And frequency response is this(just same like RMS):
And here ED-29589-000 no-dampered frequency response graph of Etymotic research ER4P.
And here TWFK-30017-000 no-damped frequency response graph of GH-ERC-DMS.
Its big differences may came from single or dual armature structure. But it could be checked response of 30265 will be wider than 29589, but 30265 is not similar either 29589 and 30017. 30017 seems extended version of 29589.
Now I don’t have real product of ER610, my review will be continued when it came to me in 2 or 3 weeks later.