The different systems are often not compatible with each other. So you can only use the matching glass bottles for the Crystal, because the bottles can be placed in the matching insert (clearly visible, silver-coloured, on the product picture) and then the upper part of the device (attachment) pressed down onto the bottle to fit perfectly. I don't know whether there are suitable plastic Crystal bottles. I haven't done any research on this either. The filling quantity is actually one of the differences between the devices. The cylinders can be bought and exchanged in various shops. When you buy a brand new cylinder, you pay a deposit of around 10 francs, which you then no longer have to pay when you exchange it (empty bottle for a full bottle). The easiest way to compare the various SodaStream devices is to do a Google image search with the search term "sodastream device overview".