The main tube is 2" x 0.035", I weigh 175lbs and the wheelbase is 60". For a longer wheelbase, or a heavier rider I think the main tube could be inadequate.
Weight as shown here is 24lbs, 5 oz. (I have since put fatter, heavier, but faster tires on it.)
I've never had good luck with sling bottom seats before, but this one is different. Besides the adjustability, there is a breathable pad containing 2" of open cell foam. Unlike other all mesh seats I've seen, this one is open behind the glutes. I believe this allows the muscles to work more efficiently.
BTW the funky rear brake described there works flawlessly. Feels like any good Canti setup. Squealed like a stuck pig the 1st time I used it, so I thought I'd screwed up. Then I remembered that Mafac's needed 2-3 times the toe-in of modern brakes.