I was ask to do a Field test on a 8,10, and 12 inch concentric coil a few years back and I really like the 8 and the 12 inch and did super great for coin hunting I felt and would buy one in a heart beat of these I did the Field test on, but they are not going to be made from what i hear. The reason I feel is the cost to make them and then to sell enough of them to to get the company's money back maybe slim. We see more people buying the FBS detectors then the BBS.
Now there is another company make a 8 inch concentric coil too and I tried one and thought it could be bad so it went back and got another one and it too was not something I would use much for my coin hunting so I sold it. It sure wasn't like the concentric coil I had tried before.
One of the things on the 12 inch concentric coil I did the Field test on that blew me away was at a old home site where I pounded the front yard with my Explorer 11 and stock coil until I never found anything more and tried the Sovereign with the Concentric 12 inch coil and popped out 2 IH and 5 more Wheaties that gave nice signals. Some of this can be I know the Sovereign tones well plus being a concentric coil it could separate better.