What are the disadvantages to using a curved secondary mount?
A straight-vane spider has a big mechanical stiffness advantage over any curved design. The tensioned vanes permit the spider to be thin, yet strong. With curved designs, the loss of rigidity must be made up by using thicker or wider vanes. Some types of curved designs with thick vanes will create several times as much total spider diffraction. The linear spikes will be gone, but there will be a wide diffraction glow around objects like bright planets. The ProtoStar curved arch largely eliminates this problem with a pre-stressed, tapered, arch design that is highly efficient compared to a simple bent piece of flat stock metal. Thin stainless steel is used to keep the total diffraction (or obstruction ratio, as defined in question 6 below) about the same as our straight-vane mounts. In fact, the total diffraction is usually less than the 4-vane mounts.
