I did not have a buck come to the roar by using it blind, but then I rarely used it blind, I often used it in association with rattling.
I did have deer I could see respond to it, both positively and negatively. I think a lot of times people think the call is not working because the deer doesn't come in when they see it and call to it. If the deer can see over where you are, and he doesn't see a deer making that noise he hears, he's not going to come. Calling is best done where the deer can not see into the area where the noise is coming from, so he has to come closer to investigate.
I found that smaller bucks would tense up when they heard the sound. I had a couple mature bucks ignore it, which surprised me. I also had a 150-class ten pointer tuck his tail and sneak off. Boy that gave me confidence in the scrapes I was sitting over.
I feel good about the call, and I think it is going to be terrific in some cases, but I don't think it is going to totally change the way I hunt using calls.