These rank up there with the best tapes ever made. They are on par with the Maxell Vertex, TDK MA-R and MA-XG and Denon XG-M.
Sony also made a Sony Super Metal Master which was even more expensive and comes in an aluminum case.
I have a handfull of these which are not sealed, and I've compared them to the ones mentioned above (on tuned Naks) and they are indeed, VERY VERY good tapes!