The hf2 are wired canal earphones similar to the ER.4, but designed primarily for use with the Apple iPhone. As such, they also function as a headset and feature a connector specially designed to fit the iPhone (reduced diameter body and 4-prong 3.5 mm jack).
While the ety8 are also designed for use with the iPhone, they don’t function as a headset like the hf2. Furthermore, both the ER.4 and the ety8 are more expensive than the hf2.
The hf2 are molded from a pleasant (both to the eyes and to the touch) soft black material. However, the headset, which is located on the right cord, detracts from the overall design by being rather bulky (see pictures).
I tried the hf2 with other devices and the earphones worked properly, but the headset only worked with the iPhone, and should work with some Blackberry devices (like the Curve). As for Nokia N-series devices (like the N95, N81 and N810), the hf2 can be used via the remote control (it should not be connected directly).
When used properly, the hf2 sound absolutely fantastic and attenuate outside noise extremely well. In addition, they operate exactly like the earphones/headset supplied with the iPhone.
I noticed an extremely mild difference in sound quality between the newer hf2 and my older (both design and age) ER.4. I prefer the high-end on the hf2, but I prefer the low-end on my ER.4. In fact, the transducers in the hf2 appear to have a similar frequency response the ones in the ety8.
The verdict? Great performance and great value – thumbs up for the hf2.