I put the speaker on a variety of flat surfaces and it sounds pretty good in that position and plays loud for its size. The only problem is that when you crank up the volume -- there are volume controls on the speaker, though no transport controls or pause/play button -- the speaker vibrates and can end up moving around a bit. It also distorts. Badly at times.
For instance, when I played the Black Keys "Fever" at higher volumes it got pretty crunchy. As did anything with a lot of bass. Prince's "FallInLove2Nite" sounded OK at lower volumes but then warbled when I took it up to 80 or 90 percent. The speaker just isn't equipped with the digital processing to keep the sound from rolling off. The larger Voombox Outdoor does a better job of handling bigger bass, but I can't say the bass on that speaker is all that tight.
On a more positive note, if you don't push the Voombox Travel too hard, it sounds decent, particularly in the mid-range (all these little speakers tend to be strongest with voices and acoustical material). I tried playing around with the placement of the speaker and came to the conclusion that it would probably sound best -- and stay in place most securely -- if you attached a thick rubber band to the carabiner and hung the thing from a nail in the wall.
I'm probably coming off sounding a little too critical about the Travel's sound (all these speaker are meant for casual listing), but the truth is you're not going to do too much better with a speaker this size, especially at this price point. More expensive water-resistant competitors like the Braven BRV-1 and UE Boom offer better sound, but the Voombox Travel is small enough to fit in a pocket. There's something to be said for that.
When I first started using the Voombox Travel I liked it a lot, particularly its build quality, and was leaning toward rating it 4 stars (at excellent). I also thought it sounded decent for its size and price. My only reservation about the product is that it does vibrate at high volumes and can move around on smooth, flat surfaces (such as a table). It also distorts at high volumes.
In the end, I still think it's a very good budget choice for wireless travel speakers, but understand that its sound quality will fall off if you push it too hard.