The 3D is an awesome unit, provided it's up to spec. It appears there may have been a brief time period where the calibration process done during the transition phase between Fisher and First Texas, was not up to par, hence some of the 3D's made during this time frame, were not as hot or deep as what has been expected from a CZ.
The 3D is great in older areas, and even though it may bring some modern trash into the coin/high tone ID area when running in enhanced mode, that can be alleviated by running in normal mode.
The simple 4 tone, analog features and ease of use of a 3D ( or any CZ for that matter), will stand the test of time. The main thing for a new CZ user to realize is make sure you ground balance the unit properly, do NOT run sensitivity past 3 to start ( a stable CZ is a happy CZ), and when running in discriminate mode, run in 0 setting to start. Learn ALL the sounds a CZ makes on ALL types of targets. The meter can be used, but I truly believe die hard CZ users over the years will tell you that the audio is the most important by far, and when you get your ears trained on a CZ, you will know with pretty darn good accuracy, when you have deep silver ready to be dug up.
The stock 8 inch coil is the perfect coil for that unit in my opinion and gets super depth even compared to some other units running 10 or 11 inch coils. No DD coils available so if you are a DD fan, you are out of luck. Pin pointing is a breeze with the 8 inch coil, and you don't even need to use the pin point button. But the pin point button has a great feature in how you can utilize it to size a target with it's fast re-tune and VCO. Great option to use for helping identify iron as well as getting a depth reading. Modulated audio is also a plus.
I say don't hesitate if a good deal pops up on a 3D, but guys n gals who know me on the forums know I am a huge CZ fan so I will always recommend one to be in any ones arsenal. They don't have a million bells and whistles, fancy screens and hundreds of options or programs. All they have is power, ease of set up and are built super tough.
One of the best things about a CZ is once you know how to set it up and run, you can throw away the manual. You never have to remember how to navigate through screens, what buttons to push to get what setting, etc. You can be away from a CZ for years and pick one up and set it up to run at optimal settings in 30 seconds once you have learned the unit. Super cool in my book with my fading memory !!! HA !