From what I can tell, the earlier silver ones used a gas solenoid valve in them, and it came with that nice petit torch, but at some point SIP decided to cheap out even more and swap that for the chunkier torch mine came with that has a mechanical gas valve in it. It means even more aggro if I wanted to fit a euro connector to mine.
The even earlier ones with the red casing seem to have been designed and built before SIP put the bean counters in charge of all their engineering decisions. They weren't a bad machine...... Still not GOOD machines, but a lot better than what the last of the line became.