Theory is, story is, that this coil is a bit hotter than the stock coil but the advantages are not that great unless the coil is specifically tuned to the individual machine. Some of the Treasure coast guys are using this set-up but they won't cough up who is doing the work. Can't blame them I guess. I know Hudson River Metal Detectors was doing some work on the cz-20 hotrodding it, before Sunray came up with this coil, so maybe I will contact them and see what they are up to. Last time I knew they were building their own underwater machines loosely based on the cz-20. Who knows? I just would like to get the work done before I go down there this spring. When you are talking water hunting or down at the treasure coast any little bit of added depth or even just better disc or stability is worth it since you are talking about potentially multi hundred dollar targets. I did extensive tests on my Excaliber with the Wot coils and found that the increase in depth was not dramatic, but I will take anything I can get, and the coil has more than paid for itself this fall (and then some) just with the 50% increase in ground coverage and the slight increase in depth on Gold targets, the only targets that matter to water hunters! Now, if you have a cz7a or a cz5, you have the same coil as I do on the cz-20. The Sunray coil must offer some advantage over the stock Fisher coil on your cz-5 or Sunray would not bother to sell them. Whatever that advantage is I want it for my Cz-20! My Wot coil gives me 3 to 5 inches better depth on large gold rings so if the Sunray gave me a similar result I would be VERY HAPPY. Especially if that 8 Escudo gold cob is just a couple of inches deeper than I am currently getting with the Cz-20!