For me, for some reason, my thumb doesn't engage well with most spyderholes. One time, my thumb slipped and the pressure from the lockback closed the blade down on the meaty part of my palm under my thumb giving me a good size gash. The worst part?...this happened when I was taking my wedding pictures, so not good to get blood and what not on my bride's dress, or the big bandaid I had that I was trying to hide from the camera (which made some poses look weird). The hood gives me a much more secure method of opening as it engages my thumb much better. I also prefer thumb discs. I know many don't like studs, discs, ramps, etc. because they can snag in the pocket, but I don't mind it snagging in my pocket occasionally if it allows for faster and more secure opening for me.
I don't think the Cobra Hood is a Spydie exclusive as it's really just a variant of a thumb disc, but I haven't seen people go nutso about it's similarity to a thumb disc to call it infringement on design and what not. Too touchy a subject there. I just like it because it guarantees my thumb won't slip. And with gloves, I can still engage it very easily without wondering if I'm getting enough engagement with the hole from my thumb. Oh well, guess I won't see the Cobra Hood any more. My likes often seem to counter that of the majority, so it's sometimes hard to find the ergos I like.