I looked to go down the rechargeable 12g co2 route before but found extensive trawling through the internet to show that the product is fruitless. Not only does the product not have a burst disc (unlike the buddy bottles) but it is so easy to overfill as such as small quantity of co2 is dispensed into the cylinder, it is easy to overfill. Finally, given the size of the valve in the little 12g, there is little room for actual co2. Your best bet in my opinion is just to buy disposable co2s in bulk from JSR at just 25p a pop, they are hardly expensive.