The review about this product
JBL Flip Wireless Bluetooth Speaker (White) (Electronics) I have the Braven bluetooth speaker and have heard the Jambox and the JBL flip in my opinion beats them in sound quality. And its cheaper at only $100.
You cant expect too much from such a small speaker but the JBL is surprisingly better than its competition. JBL is already a well established company in the field of speakers and put out good products.
The frequency response of the Flip is much better than the Jambox and Braven and can hit the lows much better which is a challenge for such small speakers. The Flip also gets much louder than at least the Braven. I didnt get to test loudness with the Jambox.
Only con about the Flip is the battery life. With the amplifier pushing 2x5W to the speakers, you get the loudness and good bass response, but at the price of a lower battery life at about 5 hours. Increasing the sources volume and keeping the volume lower will probably help with the battery life a little.
If you don't plan on using this speaker all day at a picnic but rather for just a few hours as you wash your car or something, then this is an excellent buy. If you do plan on using it all day, be sure to have a friend with a Flip there as well!
UPDATE (10/24/13): As with all technology, new and better things come out so fast. One big recommendation is the Bose SoundLink Mini. You would pay double the price but you definitely get double the sound. I used to think Bose is overpriced but I think this buy is worth it. The regular soundlink is okay and I dont think that one is worth it. But the size/sound ratio of the mini is outstanding.