with flux coated 0.9mm wire,i prefer the gas option though,i personally think it makes a much neater job,the only obvious drawbacks of using gas is the extra cost & if using the welder outside the gas tends to blow away so a windbreak is required,what are u planning to weld?
weldquip does the conversion kits if u use co2,he also sells the disposable type,he is the man to give u all the necessary info on clarke mig welders & consumables,he usually replies instantly & is both knowledgeable & helpful