I have maintained my mile-long, hilly and twisty gravel drive for 12 years with a box blade. I now have a rear blade that is useful for pulling in rock from the side, but snags and is easily damaged in the forest areas. I have had to recoat my drive - an obviously expensive undertaking - only twice in those 12 years, that those were thin recoats. The box blade is great for pot holes, although I only have a few, and spreads gravel from area to area to maintain a uniform appearance.
All that said, my friends who have land planes have about convinced me to blow the money to buy one. They do appear to be even better than a box blade, and, with the angled blades, would help maintain a crown. I don't have a lot of areas with crowns because of the hilly nature of the terrain, and you can crown with a box blade with careful use.