I don't know, but they seem to be well reviewed. I notice that one of the reviews says that he needed to screw into his Polks, and if there is a chance you would do that, I would look towards some HTD(?) mounts like what rmk used. If I did it over again, I probably would have got those instead of my Omni mounts (which could possibly be the most well known brand). Well, you see, a common rec you hear is to get double the weight-spec of whatever your speakers really weigh, and well these here are rated pretty solidly at 44 lbs. Just letting you know of some other options. I remember rmk said that Jeff Permanian fully encouraged him to drill into his speakers, like whatever it's no big deal. Your call of course. On my PSB, it would have been a very simple operation, the xover is attached directly to the binding post-plate (I forget what the proper name is, argh), so no fear there, and I could just temporarily remove driver to shake out the dust if I wanted to.
HTD Heavy Duty Speaker Bracket