Hi there

The little CO2 tanks are Crossman Air Gun refills, emptied of course, and the outlet hole drilled and tapped to suit a Festo fitting suitable for the gas connection.

Yes, they do sometimes cause problems with freezing, but there are loads of posts showing how to get around those.

Personally I've never experienced any icing, or loss of flow. I did find some swarf inside one once, but it hadn't caused any problems. I heard it rattling inside during a check.