I have these detectors and a few others. For freshwater hunting either the Tiger Shark or Excal 1000 get the nod. Of the two I prefer the Excal because of the depth, iron mask, and DD coil coverage. Con: The price.
The CZ20 is a good detector for fresh or saltwater also, however with Fisher being owned by Bounty Hunter's parent company the cost of repairs for warranty work is costing $$$$, if they will repair it at all since they say they don't have parts for it anymore. When mine dies, I'll deep six it.
I suggest you order the larger coil for the Tiger Shark for more coverage area per sweep. If you can still find the Clean Sweep Coil for the Tiger Shark you'd be wise to get one. Tesoro offers the same coil for another machine now and the connector is different. The coil is 18 X 3 inches and covers many inches per sweep and makes extremely fast work of a beach or land hunting. It pinpoints at the tips of the coil and is light weight. The Tiger Shark has the saltwater mode and is good at finding gold chains, even the thin ones.
HH,
Sandman