The choice and style of spider is effectively a choice of what you want to see in your star images. A straight vane causes diffraction in a 2% area. A curved vane’s diffraction is equal to its curvature, thus a 90 degree curve in a vane equals a 90 degree swath of diffraction. I've looked through curved, looped 3 and 4 vane and I put myself in the rigid 4 vane camp. My heart says the views are 'cleaner' in a curved vane system but my head says there is more total diffraction. Curved spiders are often thicker than their 3 or 4 vane counterparts which are held in tension but I feel that it comes down to what you want to see and what is most pleasing. Perhaps splitting close doubles would be preferential with a 4 vane if you move the companion out of the spike of the brighter star whereas planetary views smack bang in the centre of the eyepiece might appear better with a curved. Just my 2 vanes Regards Dannae