I buy my soda stream bottles from kmart - they are now the 100L ones and didn't work with my soda stream adapter that worked with the old 40 and 60L cylinders.
The old adapters "fit" - but the little prong that pushes the gas release valve is too short. 30 seconds of thinking about it and some tinfoil had the problem solved.
It means modification of a system that deals with the high pressure side of a CO2 gas cylinder - it works for me and I haven't killed myself. But if you try it and blow your legs off, its because you did it at your own risk, got it wrong and it aint my fault - you were warned.