I have been reading about this earphone since you mentioned it on the prior post. It seems like a great deal with amazing sound...but, a lot of negative reviews on the build quality/durability of these earphones. That is where I am always afraid about when getting an affordable product like headphones...you get what you pay for in some cases. I wonder if Logitech sacrificed some build quality in favor of sound...while Klipsch S4 does the opposite sort of speak.
Klipsch S4 uses old driver design (not armatures like UE 600) to keep price low. These old drivers are relatively small too (8.5) but good with heavy bass but suck with mid to upper frequencies (or so I have read). So, Klipsch designed these old drivers with dual magnets to help them move faster (& respond faster) along with enclosures to improve sound...thus, helping mid and high frequencies somewhat. I think that this is why S4's are so popular...they are bass heavy for sure, which is popular with most (non-audiophile) folks, but it also has half-decent mid-range and tiny bit of high range. It certainly cannot compete in the mid-range and treble with the newer armature-driven earphones.
As a reward for still using yesterday's drivers, Klipsch did a pretty good job on build quality for the S4 II (2nd generation), pretty much eliminating most of the 1st generation's issues. And kept the price reasonable.