I have posted my opinions about the Boostaroo before, and I am definitely in the minority here (no big surprise
My first decent headphones were/are a pair of Koss SportaPros. The sound that came out of these incredible little things was nothing short of amazing, especially considering their meager $19.99 pricetag. The only downside was that, at 60ohms, they taxed my headphone out of my little Panasonic PCDP to the point that I was using up my rechargable AA's rather quickly. Lo, I decide to try the little Boostaroo at my local RatShack and purchased it immediately ($14.99). It immediately brought out more from the SportaPro's, at a decent volume level, AND afforded me much
more battery life just like the ad says.
The "hiss" that so many report was not evident with the SportaPros. Since trying the Boostaroo with other phones, both more efficient (lower end) and higher impedance (higher end) ones, this has shown up. But I think that the 60ohm point is just right for the Boostaroo in that they mask this shortcoming.
It served me quite well and did not ask anything of me. Battery use was very efficient too. In my particular combination, it was money well spent until I could afford a better home amp and cans. For portable use, I have gone MD and earbuds (ultra-stealth). I have tried a few of the Airhead models, past and present, regular Airhead and TA versions, and I would not pay full price for them. Get one used for a good price and they are a decent value. Or get a DIY from one of the good people here.