Have to chime in here ...
Picked up a pair of hf-3s for a lark and travelling. They got me completely hooked on iems, and ended up buying a UM Miracle custom, and then a pair of HF-2s when I saw them go on their current $99 special at Etymotics.
The hfs are a great bang for the buck in my mind, with great isolation, and I use them for riding bicycles and motorcycles with very good comfort once I got used to them. Yeah, the Miracle stomps all over them for quality, but bang for buck the HFs definitely win. Also, I go to the HFs for workout / sweaty, and surprisingly they work better under the MC helmet as well.
Couple of things I have noticed though:
Both my pairs of HFs had something weird with a least one of the filters after initial purchase. I ended up with a rattly buzz sound in at least one side, which went away after changing the filter.
Also, I have confirmed that these need a lot of burn in. I remember my first impression on the HF3s was that they were so / so and really didn't like the distortion on the bass. After playing them for a while they grew on me, and I liked the sound better. Couldn't tell for sure whether it was me, or the phones changing. When I picked up the HF2s the (perennial) do iems need burn-in thread was on, so I've been using the HF2s for an experiment. Out of the box, they sounded horrid next to the HF3s. Very similar to the differences that I had remembered in my thoughts of the inital burn in. (relatively) poor imaging, flat soundstage, and a bass response that was quite distorted. I used a blind test and could easily pick out which one I put in my ears each time within 3-4 seconds of listening.
After 100 hrs of burn in (with me only listening to the new ones for 5 min sound checks every 10 hrs or so), sound signature / staging they are very similar. Although I think the new ones are still slightly flatter in staging. They are much more difficult to tell apart. However, I'm still able to hear significantly more noise floor on the new ones, which makes it so that I can still pick them out 100% in a blind test. We'll see if I can get them to match!
At any rate, for perspective owners, I think they are amazing IEMs with microphone that really works well, for $99 (current price HF2 on ety website) However, don't be discouraged at initial listen as they do improve quite a bit with burn in.