Disposable cartridges usually do not last very long, and are quite expensive in the long run. On a Rio 180, 600 grams of gas will not last that long. I would recommend a larger cylinder (perhaps 5 pounds (~2.2 kg)) at the very least.
In addition, the regulator and needle wheel may not be of the highest quality, so you may experience difficulty with adjusting/the stability of the CO2.
You can build one yourself, check darkblade's or oldpunk's DIY instruction threads.
It is fairly easy to find the parts in UK, a evilbay double stage regulator with UK standard bull nose CO2 tank connector, plus the BST threads solenoid, swagelok metering valve(UK evilbay).