Those old disc-plows have a place. Their niche is plowing new ground, where you don't know where the rocks and roots are. They can be a real hassle to get parts for, if it's not a big name brand. They also use less horsepower per bottom to pull. Some things to look for: brand ID, diameter of disc, bearing looseness, tail wheel center spine wear, and the missing disc scrapers. When properly maintained, these plows will plow every bit as good as a moldboard plow, plus they will cut right through a 3 inch tree root!