Pros: Home-made, excellent SQ, price, independently-controlled gain levels per channel
Cons: No charging indicator, no bass control
I bought this amp as an attempt to make my Bose OE sound a bit better. It failed to do so... simply because the Bose OE doesn't like any kind of amplification. After reading some forum posts, I decided to buy the Sony MDR-XB700 and they are mind-blowing with this amp, and a lot cheaper than the Bose OE. These love to be amplified and it really shows the PA2V2's true potential.
As for the battery life, I have used it for about 5~6 hours and the batteries are still holding their charge. I don't use it a lot to actually measure how long the batteries will last but, for me it's good enough as it is.
SQ is pretty good. Coupled with the FiiO L3 LOD cable on an iPad 2 (playing lossless tracks), the quality is insanely better than the iPad 2's built-in amplifier.
Support from the creator of this device is top-notch. I wish most sellers were as supportive as he is.
As for the draw-backs, there is no charging indicator. Gary says that if the amp is turned on, the batteries will not be over-charged but, when the unit is off, there's no way to tell if the charge is complete and he suggests not to leave it connected for over 8 hours. Not a deal-breaker for me but still, over-charging batteries by accident can result in physical damage, or worse.
Another missing thing is that there is no bass boost control. Also not a deal-breaker for me since I rather prefer natural sound that can show the headphone's potential without EQing them, which is a plus. Also, for the value, it's not an important feature anyway.
As it is, this amplifier is a great upgrade coming from a FiiO E5. Lasts longer, higher power output and SQ, and it's still portable although bigger. For $60, you can't go wrong.