The double blade has a few advantages.The double blade thing has always eluded me. Stacked blades are effectively cutting the grass twice or the top blade is not cutting at all. So that blade is basically along for the ride and putting additional load on the mower. It's sort of like having a bush hog set up incorrectly with the front higher than the back making it cut twice.
I dont think lack of star pattern is an issue. MOST commercial mowers just have a round hole and rely only on bolt clamping force. The star pattern or blades that have an index pin are usually something only seen on residential grade mowers.i strongly considered these, over a set of gators, my mother is a fanatic about clippings, starting to think i prolly should have got these, not thrilled about the lack of the star pattern, curious to see if that bolt is going to loosen or the assembly spin