Pros: Music is fuller, crisp, instruments are clearly seperated and represented. Great overall value.
Cons: Non so far.
What can I say about this device. It is simply fantastic and for the price you can't beat it I say. I currently use this with my Sennheiser IE8's, Bose IE2's and in my car connected to my stereo and it makes all the difference in the world with all 3 of these devices. I haven't figured out how to use it to bypass my sound card in my computer but I will soon. I know for sure its better than my Xi-Fi card from creative and that alone is a very high end card for a computer. I notice when using the Fiio with all my devices my music sounds fuller, more detailed, crisp in all aspects, highs, mids,lows, bass.
Things that I didn't notice before are clearly apparent now and the clarity of your music is unbelievable. I've been showing friends and coworkers how this sounds with my Bose IE2's and they are blown away with the clarity and sound stage. The Bose IE2's are a great improvement from the last gene but man with the Fiio and my Sansa Fuze it really makes them enjoyable to listen to even though I have a pair of Sennheiser IE8's (which are still far superior to the Bose) I still enjoy listening to my Bose IE2's with the Fiio, go figure ;)
One nice feature on the Fiio is the bass equalizer. Very simple 0 to 3, I only take it up to 1 though as it seems to interfere with the mids with too much bass but 1 is perfect. 0 sounds great too but its more analytical. I prefer some spice in my music opposed to a more straightforward boring sound. As I said earlier you can plug this into your computer to bypass your sound card which is another great feature and gives your more versatility and overall value. I like how the device isn't overly complicated and pretty much idiot proof.
If you are mainly using this with your mp3 player you definitely want to make sure you don't use the 3.5 jack for you headphones to connect this baby to your mp3 as that will cause the amps in the Fiio and the mp3 player to conflict. You'll have to max the volume on the Fiio while also suffering sound quality lose due to the 2 amps conflicting. Get a Line out Dock (LOD) for your device unless your mp3 has that extra port connection for the amplifier then you're set. Fiio sells (LOD)'s for Sansa, Ipod (Eww lol) and Sony Walkman. Basically the (LOD) connects to where your would normally connect your charger/music loader cable to your Sansa/Ipod and the other end connects to the amplifier; while you plug your headphones to the 2 available 3.5 jacks on the Fiio (that's another great feature).
Basically connecting your mp3 to the (LOD) completely bypasses the amplifier in your mp3 player and instead exclusively uses the amp on the Fiio. So the mp3 player is only transmitting the music to the amp, I think that will also extend the batter life of your mp3 player so you don't have to charge it as often another plus :). And as the amp on the mp3 is completely being bypassed, even if your using an mp3 player with crappy sound quality (Ipod) you will still get spectacular sound due to the Fiio.
The Fiio goes all the way up to 60 max volume and has a memory feature for the volume control. The device also has a sleep timer on it which is quite helpful in extending batter life between charges. I heard the battery can last up to 80 hours on each charge, haven't tested that yet. Finally but not least there is a key lock feature and a USB on off charge feature.
Overall I would highly recommend this to the beginner audiophile or to someone who just enjoys music and wants a cheap alternative to the higher priced amps out there. Fiio has a great reputation for sound quality and overall durability from their products, even though its made in China lol. I got mine from amazon from Micca and I've heard of them going as low as the mid $80 range. So if your looking to immerse yourself in the pure exhilaration of music then get this product, you won't be disappointed. Good luck guys and gals :).