Portable speakers are great for beefing up the sound when you are on the go. There's a growing number on the market in all shapes and sizes, and at all budget levels. Most of them allow you to connect up to your smartphone, laptop or MP3 player with ease. The RocksteadyXS from Killer Concepts claims to be the best performing portable speaker on the market. That's a bold claim from a newcomer to the scene, so let's see if it really lives up to it.