Pressure Switch - 2L tank, compressior. Dont use a compressior on a bottle of coke plastic crappy thing. Plastic bottles on AVERAGE only go up to about 100psi before things go bang.
Use ur 690g buffer thing with the compressior. - Sorted.

Depends what ur doing. Doe Demo - maybe the 2 x 2L bottles as its quieter. But for battle - the compressior.

Mr Stu
- yes that bottle in Chris picture is a 600g Co2 bottle. Same bottle that Rip, DTk, FlowRate, Cut-Let, G2, Prince of Awe, New PLF, MiniMoth etc all use.