Pros: Very robust and sturdy yet light, great design on volume knob to ensure it's not accidentally moved, great boost to overall sound quality
Cons: Drains your iPod battery faster when using the L9 cable. Unit power source should have been given a 1500mAh instead of an 800mAh battery
Quality - In terms of amp build quality, the unit is made up of metal and plastic which isn't really a bad thing. It makes the unit light yet very sturdy. The fit and finish of the metal covers are excellent, very tight and does not move around or jiggle when installed onto the unit. The only gripe I have about is the quality of the battery included in the package. They could have easily stuck in a 1500 mAh instead of the 800 mAh unit inside. Nevertheless, I can easily go to my local cell phone dealer and look for a higher capacity battery of the same spec and replace it myself for a little less than $10. If it wasn't for the added cost of upgrading the battery as well as it's shortish (14+ hours) life, the quality would have been given full marks.
Design - The black covers of the amp are made of metal while the body or chassis itself is made of plastic. The plastic is given a faux aluminum look, and it pulls it off nicely. The color combination of black and aluminum comes off very well. The switches are well thought out as they are easily set but not to the point where it will accidentally be moved when placed in your pocket. Another great design is the protective brace around the volume knob, this actually also ensures that the knob does not move (no sudden volume changes when mobile) when your lugging it around in your pocket. At the same time it protects it from being damaged, since having a simple knob on top would lead it to flex left to right or up and down when in your pocket. The use of a cell phone battery is also a great design choice, it gives the flexibility of actually re-placing (all you need is to buy a cheap spare) and even upgrading the battery unit itself.
Audio Quality - I actually purchased these together with my Sennheiser HD518, I was dead set on picking up the E7 since I was interested with its DAC function and future upgrade factor with the E9 combo. After listening to both amps I was blown away by the robust, full and warm sounds that the E11 amp produced versus the E7. This unit is actually very powerful for its size and price, it has two settings inside the unit itself, low and high power plus an additional setting (outside the unit) of low and high gain as well as two levels of EQ boost. With my HD518 I have it set to high power, low gain and an EQ boost of 1. The amp makes the bass of my HP tighter, fuller and richer while not diluting the mids or the highs. Soundstage is broadened by a bit and overall sound produced is warm.
Value - The E11 would have been given full marks if it wasn't for the weakish battery included in the package, resulting in an additional (yet cheap) cost to upgrade. For the price I would definitely recommend this great portable amp to anyone. Another reason for lowering the overall value is with the L9 cable any iPod is drained of its battery faster, thus limiting the time spent listening to music. Of course a simple remedy would be to use an L2 cable (included in package).
Overall - The E11 is an audiophiles (entry to mid level) portable dream amp! It's cheap and delivers outstanding sound!
NOTE - Best settings for the FIIO E11:
1) Warmer Sound with Bass - High Power / Low Gain / 2 EQ (1 EQ if you want less bass)
2) Clear Mids and Highs with some Bass - Low Power / High gain / 2 EQ (1 EQ if you want less bass)
3) Max sound - High Power / High gain / 2 EQ
I personally prefer setting #1, since setting it at low gain actually reduces any 'hissing' noise. This setting also makex the sound stage well rounded and the tone warmer overall.