Well, I had them for a while (until they broke), and really enjoyed them. They do not extend very high, but the bass is very good (if anything, the bass quantity is light, but it's tight and fast). The mids are really nice, actually I preferred them over my SF5pro. Isolation is good, and comfort, for me anyway, was very good too. But as ClieOS said, there are many alternatives at this price point. For example, a couple of days ago, I bought the Radiopaq Jazz for about 20$ and I'm pretty sure that many people would prefer them over the SF3. They have much better extension (both end), but they have a little recessed mids for my liking (coming from mid-froward SM3 anyway).
I have this IEM and the biggest problem with them is the pretty difficult fitment of these IEM's--even the Comply T-500 foam ear tips only provide reasonable (at best) fit into my ears. Now, if I had custom ear tips, they would probably sound way better, but custom ear tips cost way too much money!
They are great for $45. I also preferred them over their older brother, Super.fi 5 Pro. But I would recommend stretching your budget a bit to $79 and getting Hifiman RE0 and Sunrise X-scape - they are much better sounding than the Super.fi 3 at only $35 more. In fact, they will probably be the sweet spot in price performance. Anything more expensive will be subject to increasingly diminishing returns.
Well, right now, I'm in my 0-50 dollar price bracket. When I have what I want here, I'll move up to 50-100. I'm only 14, so I have to manage the meager amounts of money I DO have wisely. As of now, I'm looking at Meelec M6's and ht21's as well as Brainwavz Pro Alphas.
the superfi.3's were the first iem i bought.
i really enjoyed them, i felt they were a good
introduction into the mad world of headfi :]
they have great mids, i would even go as far to say they have better mids than the TF10's
the bass is lacking but it isn't a problem unless ur a bass head
vocals sound surprisingly natural.
the fit is different from anything ur probably used, but eventually you'll get the hang of them.
the isolation is really nice. although it can be somewhat creepy not hearing anything around you when you are out (careful when crossing streets)
for 45 bucks...i say go for it. you won't be dissapointed