It looks almost exactly like the portable bluetooth Jawbone Jambox but has the great virtue of being half the price. Its quite a bit bigger and heavier than the Jambox, so you'd expect a deeper and richer sound, more bass maybe. But less portability doesn't come with better sound.
While small portable speakers by Jawbone, Fox L, and Bose, cant match audiophile standards, they do provide a solid full sound.
Amethyst comes no where close to doing so. With the exception of some acoustic songs, Amethyst distorts music by pushing some frequencies far harder than others, and lacking base -- even in not very demanding music, such as classic rock and some pop, the sound kind off 'falls apart'. The base is weak, which is often a problem with portables, but some of mid-range frequencies are overly strong and spring forward in a weird way I've never heard before. for classical music is sounds colourless, or without out vibrancy. I want to say the sound is tin-like, but that's not really it.
From £50 to £100 is a big jump, but assuming you'll keep the portable speaker for a few years its worth the investment. And if you cant spend more than £50, give Elf or a non-blue tooth portable a try.