We talked a few times about Metax here on the CR list (in reference of course to such vintage topics as the somewhat sloppy Crescent bikes, stainless tubes smoked into Nervex lugs and then the joints painted over "neatly." I saw at least two of these frames in Larry Black's stash.)
I have not heard how readily or not this tubing will rust or how it fares in "real life" conditions, but it was picked up by a few custom and small production builders...I recall that Ibis used Metax for chainstays and a now defunct Boston area company called Rhygin based their entire initial line around Metax.
Mark Bulgier has pics on his web site of the fully lugged Metax frame he built. I have a couple sets sitting around for future use(?)
Dale Brown
Greensboro, NC