I own the earlier version of the AirHead portable amp.  Different packaging, and  uses 2 AA batteries.  I purchased it used after I had my Benchmark HPA2 stolen.  The HPA2 is a headphone amp on a little PC board mounted to a 1/4" jack, and I believe it is now out of production.  I had mounted it in a small box with a DC/DC converter to provide the required supply voltages from a 9V battery.  So, technically, it wasn't a "portable" amp, but I made it into one. 
 
I mention all of that because this might not be a fair comparison.  The HPA2 was simply a glorious sounding headphone amp, and I miss it still.  I got the TotalAirHead to replace its loss.  While the TAH is nice, it doesn't come close to the HPA2.  Even with the rather interesting "processor" switched in (designed to get the sound out of the inside of your head), it has lower impact, less dynamics, and less bass than the HPA2. 
 
I still use the TAH occasionally, but frankly, the concept of a portable headphone amp is just too cumbersome.  My portable use is either iPhone or iPod, and usually stuffed in a pocket.  Another box is just a pain, and though an audible improvement, the convenience isn't there.  However, I do use an amp when stationary using the same sources.  My current favorite is a custom amp I made, and it does make the TAH pale by comparison. 
 
So, this is a luke-warm review.  Perhaps the current version is better, hopefully worth the hassle of porting it around.  One feature I wish I had on the TAH is auto shut off with silence.  I almost always forget and leave it on to eat its batteries. 

I've owned a pair of SR-80s since 1996 when my old Yamaha phones collapsed beyond repair. I auditioned a pair of SR-60s at a local high-end store, and when I was ready, got a pair.  I was very disappointed!  It wasn't at all the sound I had heard in the audition.  I was unhappy enough to return them, and in a newsgroup (remember them?) complained about my experience.  Group members had been praising the SR-60s at the time, and I couldn't get behind that.  To my surprise, I got an email from Joe Grado asking for my shipping address!  He offered me a pair of the SR-80s, said if I liked them, I could pay for them, and if not, give them to somebody else.  Can you imagine that?  Needless to say, after listening to them for a few weeks, I sent them a check for payment in full. 
 
I've owned that pair ever since. They've traveled, been outside in the cold, rain, and sun.  I changed the ear paids to Sennheiser pads, replaced the cord myself once, then had Grado do it twice.  But I still have them, still use them almost every day.  They are very affected by the output impedance of the amp that drives them.  They're ok in an iPod, but fantastic if you hit them with a good solid low Z source.  
 
They're pleasant, soothing, as spacious to listen to, but I can't mix on them.  I do some filed recording, and they just make everything sound TOO good.  But for pleasure, they're my choice. 
 
The cord is weak spot.  It's thick and in cold temperatures acts as stiff as a garden hose.  The strain relief at the ear cups is just a blob of glue, which pops off and then you break a wire in the cup.  My own replacement was Mogami Neglex wire, which held up better, but wasn't really headphone wire.  The stock pads from the 1990s were hot, and the on-ear Sennheiser HD414 pads fit fine, and though you lose a bit of the top and bottom, still retain the character of the original phones.  When I got them back from repair, they had black pads installed, similar to the 414 pads.  Nice, worked well, but dissolved in a few years.  So, I'm back to the 414 pads...for now.  I'm due to send these in for a rehab soon. 
 
I recently auditioned a bunch of headphones back at that original high-end store.  The sound of the SR-80s still beat even the $600 Sennheisers (don't recall the model), but the amp used was pretty much junk, and my amp is way better.  But today's SR-80s are pretty much the same as the mid 1990s ones I have, if perhaps a bit less "weathered". 
 
 

I'm on my third pair of these, and that's mostly because I'm hard on them. Sound is fairly uncolored, though brighter than my reference Grado SR-80s.  They respond well to being driven by a decent amplifier. 
 
The trick to getting good bass out of these, like most in-ear units, is getting a good seal.  They come with several sizes of pads, for me the larges works.  Without a good seal, you get poor bass and low isolation, but WITH a seal, wow!
 
The mic works well on my iPhone 3G and 4G, the control button could be more positive, but once you learn where it is and how hard to press it, it's ok. 
 
The downside to these is the construction, which is a bit flimsy.  I've had the cord break at the plug entrance, had to replace the plug.  I had another cord break at the mic/switch when I got the cord snagged and tugged it.  Otherwise, at the price, they're disposable. 
 
Which brings me to price.  At their list of $99, not a great value.  Good sound, but not quality.  But, who pays list?  Got mine on Amazon for $35 for the first pair, $18 for the second pair, and $25 for the third pair from independent sellers.  All came in the original Sennheiser packaging, all sounded identical. 
 
Best sounding $25 headset out there, no question!  At $100, still good sound, not a good value.