I purchased this and four other brands/models because I wanted to hear with my own ears which ones were the best in this micro portable speaker category.
The ones I tried were:
X-Mini Max II Capsule Speakers (White)
X-Mini II Capsule Speaker (Red)
Satechi SD Mini Portable Pocket Speaker
iHome iHM60LT Rechargeable Mini Speaker (Blue Translucent)
iTour-POP Ultra Portable Rechargeable Speaker
I did not include the Altec Lansing iM-237 Orbit Speaker since it is not rechargeable.
Sound quality, on a scale of 1 to 10, with 10 being the best of the group, and 1 being the built-in speaker in an iPhone or iPod Touch:
iTour: 10/10
iHome: 8.5/10
Satechi: 7
X-Mini II: 7
X-Mini Max II: 4
The iTour-POP wins it, no contest really. Amazing full sound and low distortion from a speaker this size. It's a little bigger in diameter than the others, but not as tall. Stays put, even at high volume. The next three all sound pretty good, if you didn't hear them side by side with the others, you'd be pretty satisfied with purchasing any of them. These three all suffer from 'walking' across the table at high volume, the bass thumps just make them jump a little with every beat, with the iHome being the worst at that. Not a huge deal, but it could drag itself and your $150 Nano of the counter and onto the floor... The Satechi is the only one with the built-in SD slot, which is pretty cool.
Finally, the X-Mini Max II: what a disapointment, horrible sound quality compared to the rest, especially the lower frequencies. Very tinny and distorts more than the others. Cross this one off your list.