No two pressings made at the same time will sound the same. So what they do is buy 30-40 copies of the same album, hear them all and keep only those that sound good. They don’t have any proprietary cleaning process. They do the usual standard cleaning. So what they will do is buy 30-40 copies of the first press of say for example Rumors. And sell you only those that sound good. The rest are discarded.
I have to admit their copies sound wonderful. None of the first press NM copies I have sound anywhere near to their copies of the same album. Yes, it’s a huge price you pay for it.