Without looking at any of those videos I can safely say any flux core welder in that price range will produce nice bird **** welds on steel. You will need to convert it to gas to get any kind of decent welds.
140 amps is not much for welding aluminum. Might be able to weld 1/8" material. The last Lincoln welder with a spool gun I owned was 250 amps AC or DC. I used it to repair my truck equipment when needed... trailer rails, brackets, fuel tanks and the like. I needed all of that amperage. A 140 amp machine will be severely limited in the materials it can weld.
