I have the CZ7a Pro now and HAD a Cortes. Youll find the Cortes a totally different animal from the Fisher.
It is A LOT easier to swing for long periods and that makes a difference, IMHO. The balance is way different. It is also smooth and the VDI numbering is different from the Fisher. The coil covers more ground than the 8" on the CZ, too. These are the immediate things you notice.
Next youll see that the screen is small compared to the Fisher. Okay, "tiny" is a better adjective. But there is only one reason to have that screen - the VDI display. It's all youre gonna look at after a while, although the "graph" display is useful too. And, the Cortes has the audio/graphic "SUM" mode, a real boon when you get used to it.
Once you use it for a while, though, I doubt that youll be impressed with the depth of the Cortes compared to the Fisher. Not that it cant go deep enough. It suits my style, as Im a "cruizer", and it has enough depth for 80% of ANY hunting you'll do.
But, the Fisher is just hotter and it has adjustable GB. I think Tesoro shouldve given the Cortes a single turn Manual GB, though (all that 3 3/4 turn stuff is nonsense). It would have made a good unit even better.
But, bottom line, it isnt the deepest detector on the market and Id say it probably isnt in the CZ's class, even. So, if your after old buttons and little bits of rusty, half eaten relicy stuff from 12" down, well, better get a Tejon or Vaquero. Or just keep the CZ.
Personally, for my style of hunting, the Cortes is a better choice and I plan to get another. But if you want a detector that will be as hot in the relic fields as it is in the city park - keep the Fisher. Then get an Ace 250 to play around with and satisfy your need to experiment. Its a lot less money, does an unbelievable job and you can get 75% of your money back in a snap, should you decide to sell it later.