Please note that this is not a real Theremin, it's a "toy-theremin".
It's very good for the price, and it sounds amazing through a guitar amp. The cons: you can't control the pitch as you would with a real theremin where you have two axes to control pitch and volume.
It's however very nice to experiment with and add accents to tunes, but don't expect to get the exact same sound twice as it's quite hard to control.
Also if you set it near any other electronic device (any other amps, a PA, mobile phone, etc), it will interfere with its sound.
However, as I was saying, for the price it's a fun instrument to play with. The shell is also quite sturdy and it comes with a soft plastic case. You'll need a tiny screwdriver to set it up. The power supply is a battery, so it's fully portable.