And love it to death. I use a CZ-5 on land, so I didn't have to "learn" a new machine. Yes, the CZ-20 looses a little sensitivity by being locked into SALT mode. Oh well. No skin off my back, as I'm not looking for fine chains anyway. The CZ-20 is built like a tank, although it is heavy. That changes in the water, as the control-box floats. I'd advise that you get a spare O-ring for the battery compartment, and some silicone grease or vaseline (I use vaseline) to help the o-ring seal. The headphones and coil are hard-wired to the unit.
I don't have an Excal or Infinium. From what I've read about the Excal, the discrimination is superior to the CZ-20, BUT, the quality of manufactoring the unit is lacking. Wires come apart, knobs come off, it needs a different stem, etc.
I can't really comment on the Infinium. I haven't used one, and haven't really read any material about it.
Fisher is releasing an updated version of the CZ-20 hopefully later this year. They're going to call it the CZ-21. From what I've heard, the only change will be a different pinpoint cover.