Anyone used this old Harris gas-saver?

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Just got this "Harris Calorific 64-2" on ebay, couldn't resist because it's old and funky, made of cast iron. I like old tools. Bought it even though I already had a very good gas saver, a Weldit W-101 from the '70s I think. (The Weldit is actually Mario Confente's old gas-saver!)

The Harris seems like it may not be very good at it's job, unless I'm just not doing it right? It doesn't shut both fuel and O2 off completely at the same time. There are adjusting screws for both valves, but it seems like no matter how I adjust it, one side or the other is left cracked open just a tiny bit. Maybe there's a sweet spot where both valves are completely off, but it must be a super-narrow sweet spot, because I haven't been able to hit it. So I left it where the O2 is still leaking a little when the torch is hung up. So at the moment, I can only use it briefly then go and turn the bottles off, not something I'd want to leave running for a full shift of work. Not that I, a retired hobbyist, ever do a full shift anymore, but still, I'd like it to work right and not waste gas.

The Weldit appears to be a better design. It really shuts both lines off when you hang the torch. Judging from the looks, I think the Harris may be much older. I'm getting zero relevant hits when I search that model number.

Any ideas? I might hook it up to a torch that uses my oxygen concentrator instead of bottled O2, and have it turn off only the fuel when I hang the torch, and leave the O2 running a little. I know that's not the recommended way to turn a torch off, but O2 concentrators don't like it when you turn the torch valve off. They freak out, and soon a nurse comes running in! Kidding but these concentrators are medical devices and a patient might die if the O2 stops flowing, so the alarm is understandable in their normal usage.