The coil will handle nasty mineralized dirt about as good as any other large concentric coil. I'm lucky to have pretty neutral soil in my area. The wide scan and/or smaller coil might be a good choice for that dirt you speak of.
As far as heavy brush and plowed fields, I love this coil when I use it. If you have deep furrows in them fields, the large coil might not get between them as well as your smaller coil does. You can get hung up in thick woods, but that is true of most any coil if the going gets too thick. The doughnut style coil only has the center opening for getting hung up versus several openings in the spider style coil. I have no problem in chattering. I have used it with a Pantera, Toltec 100 and Bandido with GB, but also with a Shadow X2 that does not have GB and the coil works great on all the machines!
You probably overlooked it, because it is not 'new and improved', but that doesn't always prove out in performance. I have found that one of the easiest, cheapest and sometimes best ways to upgrade a detector, is not buy buying the next model, but by changing out the coil for another size...be it smaller or bigger. The areas I normally hunt are open pasture, plowed fields and woods and I love a larger and preferably concentric coil. Ya might want to give it a try, I bet you like it and like it alot! Good Luck