The older CD1e's use piezos rather than a true compression driver.
From what I've "heard" the newest CD1e's (as in, produced in the last couple months) are using actual compression drivers now though.
But I'm guessing if you're buying used...they won't be the newest version available.
Anyways...the horn bodies on one of the CD1e's are supposed to be pretty good in and of itself. Can't remember if it's the mini or full body, but some people have used that horn body with regular compression drivers with great results.
The downfall of the CD1e's is the drive unit being piezo. Just not the same quality of sound produced by most true compression drivers. Doesn't have quite as high of sensitivity either.